Systems and methods for electrosurgical tissue treatment

ABSTRACT

Systems and methods are provided for applying a high frequency voltage in the presence of an electrically conductive fluid. High frequency voltage is then applied between the active electrode(s) and one or more return electrode(s) to volumetrically remove or ablate at least a portion of the target tissue. In one embodiment a tissue treatment surface includes spacers or a chamber for containing the electrodes.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 09/457,201, filed Dec. 06, 1999, which is acontinuation-in-part of U.S. patent application Ser. No. 09/248,763,filed Feb. 12, 1999, now U.S. Pat. No. 6,149,620, which claims thebenefit of U.S. Provisional Application Nos. 60/096,150 and 60/098,122,filed Aug. 11, 1998 and Aug. 27, 1998, respectively. ProvisionalApplication No. 60/096,150 filed Aug. 11, 1998, is acontinuation-in-part of U.S. patent application Ser. No. 08/990,374filed Dec. 15, 1997, now U.S. Pat. No. 6,109,268, which is acontinuation-in-part of U.S. patent application Ser. No. 08/485,219filed Jun. 7, 1995, now U.S. Pat. No. 5,697,281. Provisional ApplicationNo. 60/098,122 filed Aug. 27, 1998, is a continuation-in-part of U.S.patent application Ser. No. 08/795,686, filed Feb. 5, 1997, now U.S.Pat. No. 5,871,469, the complete disclosures of which are incorporatedherein by reference for all purposes.

The present invention is also related to commonly assigned co-pendingU.S. patent application Ser. No. 09/177,861, filed Oct. 23, 1998, nowU.S. Pat. No. 6,066,134, and application Ser .No. 08/977,845, filed Nov.25, 1997, now U.S. Pat. No. 6,210,402, which is a continuation-in-partof application Ser. No. 08/562,332, filed Nov. 22, 1995, now U.S. Pat.No. 6,024,733, and U.S. patent application Ser. No. 09/010,382, filedJan. 21, 1998, now U.S. Pat. No. 6,190,381, the complete disclosure ofwhich is incorporated herein by reference. The present invention is alsorelated to commonly assigned co-pending U.S. patent application Ser. No.09/162,117, filed Sep. 28, 1998, now U.S. Pat. No. 6,117,109, patentapplication Ser. Nos. 09/109,219, now abandoned, 09/058,571, now U.S.Pat. No. 6,142,992, 08/874,173, now U.S. Pat. No. 6,179,824, and09/002,315, now U.S. Pat. No. 6,183,469, filed on Jun. 30, 1998, Apr.10, 1998, Jun. 13, 1997, and Jan. 2, 1998, respectively and U.S. patentapplication Ser. No. 09/054,323, filed on Apr. 2, 1998, now U.S. Pat.No. 6,063,079, and U.S. patent application Ser. No. 09/032,375, filedFeb. 27, 1998, now U.S. Pat. No. 6,355,032, 08/942,580, filed on Oct. 2,1997, now U.S. Pat. No. 6,159,194, U.S. patent application Ser. No.08/753,227, filed on Nov. 22, 1996, now U.S. Pat. No. 5,873,855, U.S.patent application Ser. No. 08/687,792, filed on Jul. 18, 1996, now U.S.Pat. No. 5,843,019, the complete disclosures of which are incorporatedherein by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electrosurgeryand, more particularly, to surgical devices and methods which employhigh frequency voltage to cut and ablate body tissue.

Conventional electrosurgical methods are widely used since theygenerally reduce patient bleeding associated with tissue cuttingoperations and improve the surgeon's visibility. These traditionalelectrosurgical techniques for treatment have typically relied onthermal methods to rapidly heat and vaporize liquid within tissue and tocause cellular destruction. In conventional monopolar electrosurgery,for example, electric current is directed along a defined path from theexposed or active electrode through the patient's body to the returnelectrode, which is externally attached to a suitable location on thepatient's skin. In addition, since the defined path through thepatient's body has a relatively high electrical impedance, large voltagedifferences must typically be applied between the active and returnelectrodes to generate a current suitable for cutting or coagulation ofthe target tissue. This current, however, may inadvertently flow alonglocalized pathways in the body having less impedance than the definedelectrical path. This situation will substantially increase the currentflowing through these paths, possibly causing damage to or destroyingtissue along and surrounding this pathway.

Bipolar electrosurgical devices have an inherent advantage overmonopolar devices because the return current path does not flow throughthe patient beyond the immediate site of application of the bipolarelectrodes. In bipolar devices, both the active and return electrode aretypically exposed so that they may both contact tissue, therebyproviding a return current path from the active to the return electrodethrough the tissue. One drawback with this configuration, however, isthat the return electrode may cause tissue desiccation or destruction atits contact point with the patient's tissue.

Another limitation of conventional bipolar and monopolar electrosurgerydevices is that they are not suitable for the precise removal (i.e.,ablation) or tissue. For example, conventional electrosurgical cuttingdevices typically operate by creating a voltage difference between theactive electrode and the target tissue, causing an electrical arc toform across the physical gap between the electrode and tissue. At thepoint of contact of the electric arcs with tissue, rapid tissue heatingoccurs due to high current density between the electrode and tissue.This high current density causes cellular fluids to rapidly vaporizeinto steam, thereby producing a “cutting effect” along the pathway oflocalized tissue heating. The tissue is parted along the pathway ofevaporated cellular fluid, inducing undesirable collateral tissue damagein regions surrounding the target tissue site.

The use of electrosurgical procedures (both monopolar and bipolar) inelectrically conductive environments can be further problematic. Forexample, many arthroscopic procedures require flushing of the region tobe treated with isotonic saline, both to maintain an isotonicenvironment and to keep the field of view clear. However, the presenceof saline, which is a highly conductive electrolyte, can cause shortingof the active electrode(s) in conventional monopolar and bipolarelectrosurgery. Such shorting causes unnecessary heating in thetreatment environment and can further cause non-specific tissuedestruction.

Present electrosurgical techniques used for tissue ablation also sufferfrom an inability to control the depth of necrosis in the tissue beingtreated. Most electrosurgical devices rely on creation of an electricarc between the treating electrode and the tissue being cut or ablatedto cause the desired localized heating. Such arcs, however, often createvery high temperatures causing a depth of necrosis greater than 500 μm,frequently greater than 800 μm, and sometimes as great as 1700 μm. Theinability to control such depth of necrosis is a significantdisadvantage in using electrosurgical techniques for tissue ablation,particularly in arthroscopic procedures for ablating and/or reshapingfibrocartilage, articular cartilage, meniscal tissue, and the like.

In an effort to overcome at least some of these limitations ofelectrosurgery, laser apparatus have been developed for use inarthroscopic and other surgical procedures. Lasers do not suffer fromelectrical shorting in conductive environments, and certain types oflasers allow for very controlled cutting with limited depth of necrosis.Despite these advantages, laser devices suffer from their own set ofdeficiencies. In the first place, laser equipment can be very expensivebecause of the costs associated with the laser light sources. Moreover,those lasers which permit acceptable depths of necrosis (such as excimerlasers, erbium:YAG lasers, and the like) provide a very low volumetricablation rate, which is a particular disadvantage in cutting andablation of fibrocartilage, articular cartilage, and meniscal tissue.The holmium:YAG and Nd:YAG lasers provide much higher volumetricablation rates, but are much less able to control depth of necrosis thanare the slower laser devices. The CO₂ lasers provide high rate ofablation and low depth of tissue necrosis, but cannot operate in aliquid-filled cavity.

Excimer lasers, which operate in an ultraviolet wavelength, causephotodissociation of human tissue, commonly referred to as coldablation. Through this mechanism, organic molecules can be disintegratedinto light hydrocarbon gases that are removed from the target site. Suchphotodissociation reduces the likelihood of thermal damage to tissueoutside of the target site. Although promising, excimer lasers must beoperated in pulses so that ablation plumes created during operation canclear. This prevents excessive secondary heating of the plume ofablation products which can increase the likelihood of collateral tissuedamage as well as a decrease in the rate of ablation. Unfortunately, thepulsed mode of operation reduces the volumetric ablation rate, which mayincrease the time spent in surgery.

SUMMARY OF THE INVENTION

The present invention provides systems, apparatus and methods forselectively applying electrical energy to body tissue. In particular,systems and methods are provided for applying a high frequency voltagein the presence of an electrically conductive fluid to create arelatively low-temperature plasma for ablation of tissue adjacent to, orin contact with, the plasma.

In one embodiment, the method of the present invention comprisespositioning an electrosurgical probe or catheter adjacent the targetsite so that one or more active electrode(s) are brought into contactwith, or close proximity to, a target tissue in the presence ofelectrically conductive fluid. The electrically conductive fluid may bedelivered directly to the active electrode(s) and the target tissue, orthe entire target site may be submersed within the conductive fluid.High frequency voltage is then applied between the active electrode(s)and one or more return electrode(s) to generate a plasma adjacent to theactive electrode(s) while maintaining a low temperature in the activeelectrode(s). At least a portion of the target tissue is volumetricallyremoved or ablated. The high frequency voltage generates electric fieldsaround the active electrode(s) with sufficient energy to ionize theconductive fluid adjacent to the active electrode(s). Within the ionizedgas or plasma, free electrons are accelerated, and electron-atomscollisions liberate more electrons, and the process cascades until theplasma contains sufficient energy to break apart the tissue molecules,causing molecular dissociation and ablation of the target tissue.

In a specific configuration the electrosurgical probe comprises platinumor platinum-iridium alloy electrodes. Typically, the platinum-iridiumelectrodes comprise between approximately 1% and 30%, and preferablybetween 5% and 15% iridium to mechanically strengthen the electrodes.Applicants have found that the platinum/platinum-iridium electrodesprovide more efficient ionization of the conductive fluid, less thermalheating of surrounding tissue, and overall superior ablation. Becauseplatinum has a low thermal conductivity and low resistivity, heatproduction is minimized and there is a more efficient transfer of energyinto the conductive fluid to create the plasma. As an additionalbenefit, Applicants have found that platinum/platinum-iridium electrodeshave better corrosion properties and oxidation properties in thepresence of the conductive fluid over other electrode materials.

In some embodiments, the high frequency voltage applied to the activeelectrode(s) is sufficient to non-thermally vaporize the electricallyconductive fluid (e.g., gel or saline) between the active electrode(s)and the tissue. Within the vaporized fluid, an ionized plasma is formedand charged particles (e.g., electrons) are accelerated towards thetissue to cause the molecular breakdown or disintegration of severalcell layers of the tissue. This molecular dissociation is accompanied bythe volumetric removal of the tissue. The short range of the acceleratedcharged particles within the plasma layer confines the moleculardissociation process to the surface layer to minimize damage andnecrosis to the surrounding and underlying tissue. This process can beprecisely controlled to effect the volumetric removal of tissue as thinas 10 to 150 microns with minimal heating of, or damage to, surroundingor underlying tissue structures. A more complete description of thisphenomena is described in commonly assigned U.S. Pat. No. 5,697,882.

In some embodiments, the tissue is ablated by directly contacting thetarget tissue with the plasma. In other embodiments, the activeelectrode(s) are spaced from the tissue a sufficient distance tominimize or avoid contact between the tissue and the plasma formedaround the active electrode(s). Applicant believes that the electronsthat carry the electrical current are hotter than the ions within theplasma. In these embodiments, contact between the heated electrons inthe plasma and the tissue is minimized as these electrons travel fromthe plasma back through the conductive fluid to the return electrode(s).The ions within the plasma will have sufficient energy, however, undercertain conditions such as higher voltages, to accelerate beyond theplasma to the tissue. Thus, the electrons, which are carried away fromthe target tissue, carry most of the thermal byproducts of the plasmawith them, allowing the ions to break apart the tissue molecules in asubstantially non-thermal manner.

In another embodiment, the method further includes the step ofvaporizing the electrically conductive fluid near the activeelectrode(s) into a plasma at relatively low temperatures, preferablylower than about 100° C., more preferably lower than about 80° C. Thelower temperature of the conductive fluid will further reduce any riskof undesired thermal damage to tissue surrounding the target site andprovide an even more precise tissue removal. In one aspect of theinvention, a reduced pressure environment is created around the activeelectrode(s) to lower the vaporization temperature of the conductivefluid. In other embodiments, the electrically conductive fluid itselfhas a relative low vaporization temperature (e.g., preferably belowabout 100° C. or below 80° C.) at atmospheric pressure.

In a specific configuration the method further includes the step ofmaintaining the temperature of the active electrode at a relatively lowtemperature, preferably lower than about 100° C., more preferably lowerthan about 80° C. The lower temperature of the electrodes increase theionization rate of the conductive fluid, further reduces any risk ofundesired thermal damage to tissue surrounding the target site, andprovides an even more precise tissue removal. In most embodiments, themaintaining step is carried out by using platinum or platinum-iridiumactive electrodes.

In another aspect of the invention, the present invention providesmethods and apparatus for increasing the energy level of the ionizedplasma created at the end of the electrosurgical probe. According to thepresent invention, this is accomplished by altering the conductive fluidto either increase its conductivity or to increase the quantity orstrength of the ions in the ionized plasma. In some embodiments, asaline solution with higher levels of sodium chloride than conventionalsaline (which is on the order of about 0.9% sodium chloride) e.g., onthe order of greater than 1% or between about 3% and 20%, may bedesirable. Alternatively, the invention may be used with different typesof conductive fluids that increase the power of the plasma layer by, forexample, increasing the quantity of ions in the plasma, or by providingions that have higher energy levels than sodium ions. For example, thepresent invention may be used with elements other than sodium, such aspotassium, magnesium, calcium and other metals near the left end of theperiodic chart. In addition, other electronegative elements may be usedin place of chlorine, such as fluorine.

In yet another aspect of the invention, an electrically conductive fluidhaving a reduced ionic strength or a reduced conductivity is selected.Applicant has found that these conductive fluids may facilitate theinitiation of the plasma layer in certain conditions, such as lowervoltage levels or when a suction pressure is applied near the activeelectrode(s). In a specific configuration, saline solutions havingconcentrations less than isotonic saline (i.e., less than about 0.9%sodium chloride) are used to facilitate the initiation of the plasmalayer, or to provide less aggressive ablation of tissue.

In a further aspect of the present invention, ionic particles containedin the electrically conductive fluid are selected to fluoresce specificcolors as desired by the user when used with the electrosurgical probe.In preferred embodiments, the color of fluorescence is selected tosimulate the color emitted by an excimer laser during ablation, e.g.,blue or purple. Such color will provide certain psychological benefitsto the user and patient during electrosurgery.

Apparatus according to the present invention generally include anelectrosurgical instrument having a shaft with proximal and distal ends,one or more active electrode(s) at the distal end and one or moreconnectors coupling the active electrode(s) to a source of highfrequency electrical energy. In some embodiments, the instrument willcomprise a catheter designed for percutaneous and/or transluminaldelivery. In other embodiments, the instrument will comprise a morerigid probe designed for percutaneous or direct delivery in either openprocedures or port access type procedures. In both embodiments, theapparatus will include a high frequency power supply for applying a highfrequency voltage to the active electrode(s).

The apparatus will further include a supply of electrically conductivefluid and a fluid delivery element for delivering electricallyconducting fluid to the active electrode(s) and the target site. Thefluid delivery element may be located on the instrument, e.g., a fluidlumen or tube, or it may be part of a separate instrument.Alternatively, an electrically conducting gel or spray, such as a salineelectrolyte or other conductive gel, may be applied to the target site.In this embodiment, the apparatus may not have a fluid delivery element.In both embodiments, the electrically conducting fluid will preferablygenerate a current flow path between the active electrode(s) and one ormore return electrode(s). In an exemplary embodiment, the returnelectrode is located on the instrument and spaced a sufficient distancefrom the active electrode(s) to substantially avoid or minimize currentshorting therebetween and to shield the return electrode from tissue atthe target site.

The electrosurgical instrument will preferably include an electricallyinsulating electrode support member, preferably an inorganic supportmaterial (e.g., ceramic, glass, glass/ceramic, etc.) having a tissuetreatment surface at the distal end of the instrument shaft. One or moreactive electrode(s) are coupled to, or integral with, the electrodesupport member such that the active electrode(s) are spaced from thereturn electrode. In one embodiment, the instrument includes anelectrode array having a plurality of electrically isolated activeelectrodes embedded into the electrode support member such that theactive electrodes extend about 0.0 mm to about 10 mm distally from thetissue treatment surface of the electrode support member. In thisembodiment, the probe will further include one or more lumens fordelivering electrically conductive fluid and/or aspirating the targetsite to one or more openings around the tissue treatment surface of theelectrode support member. In an exemplary embodiment, the lumen willextend through a fluid tube exterior to the probe shaft that endsproximal to the return electrode.

In a specific configuration the electrosurgical instrument comprisesplatinum or platinum-iridium electrodes. The platinum/platinum-iridiumelectrodes have a low resistivity and low thermal conductivity whichminimizes the production of heat in the electrodes and the electricallyconductive fluid and allows more electrical energy to be applieddirectly into the conductive fluid. As the electrically conductive fluidflows between the active electrode(s) and the return electrode(s), thehigh frequency voltage is sufficient to non-thermally vaporize theelectrically conductive fluid (e.g., gel or saline) between the activeelectrode(s) and the tissue. Within the vaporized fluid, an ionizedplasma is formed and charged particles (e.g., electrons) are acceleratedtowards the tissue to cause the molecular breakdown or disintegration ofseveral cell layers of the tissue.

In another variation of the invention, the inventive device may includea tissue treatment surface configuration that is adapted to eitherminimize the heating or minimize the retention of heat near targettissue located adjacent to the tissue treatment surface of the device.The electrodes of the device may be placed in chambers which areinterconnected and allow for the circulation of electrically conductivefluid over the distal end of the the device. The devices may also havesuch features as spacers placed at the tissue treatment surface andwhich extend distally of the electrodes. The inventive device mayfurther include placing one or more vents or openings on the tissuetreatment surface to prevent the accumulation of heat between the tissuetreatment surface of the device and target tissue. Moreover, the tissuetreatment surface of the device may be adapted to minimize reflection ofenergy/heat generated by the ablative process back to the target tissue.For example, the electrode support member may be constructed from amaterial that minimizes reflection of energy/heat towards the targettissue.

These and other aspects of the invention will be further evident fromthe attached drawings and description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrosurgical system incorporatinga power supply and an electrosurgical probe for treating articularcartilage according to the present invention;

FIG. 2 schematically illustrates one embodiment of a power supplyaccording to the present invention;

FIG. 3 illustrates an electrosurgical system incorporating a pluralityof active electrodes and associated current limiting elements;

FIG. 4 is a side view of an electrosurgical probe according to thepresent invention;

FIG. 5 is an enlarged detailed cross-sectional view of the working endof the electrosurgical probe of FIG. 4;

FIG. 6 is a distal end view of the probe of FIG. 4;

FIGS. 7-10 illustrates an alternative probe according to the presentinvention, incorporating an aspiration lumen;

FIG. 11 is a perspective view of yet another embodiment of anelectrosurgical probe according to the present invention;

FIG. 12 is a side cross-sectional view of the electrosurgical probe ofFIG. 11;

FIG. 13 is an enlarged detailed view of the distal end portion of theprobe of FIG. 11;

FIGS. 14 and 16 are front and end views, respectively, of the probe ofFIG. 11;

FIG. 15 illustrates a representative insulating support member of theprobe of FIG. 11;

FIG. 17 is an alternative embodiment of the active electrode for theprobe of FIG. 11;

FIG. 18 illustrates a method of ablating tissue with a probe having aplurality of active electrodes according to the present invention;

FIG. 19 illustrates a method of ablating tissue with a probe having asingle active electrode according to the present invention;

FIG. 20 is a perspective view of another electrosurgical systemincorporating a power supply, an electrosurgical probe and a supply ofelectrically conductive fluid for delivering the fluid to the targetsite;

FIG. 21 is a side view of another electrosurgical probe for use with thesystem of FIG. 20;

FIG. 22 is a distal end view of the probe of FIG. 21;

FIGS. 23-26 are distal end view of alternative probes according to thepresent invention;

FIGS. 27A-27C are cross-sectional views of the distal portions of threedifferent embodiments of an electrosurgical probe according to thepresent invention.

FIG. 28 is a cross-sectional view of the distal tip of theelectrosurgical probe, illustrating electric field lines between theactive and return electrodes;

FIG. 29 is a perspective view of an electrosurgical catheter system forremoving body structures according to the present invention;

FIG. 30 is a chart listing the boiling temperature of water at varyingpressures;

FIG. 31 depicts an electrosurgical probe having a compliant, lowpressure chamber according to the present invention;

FIG. 32 lists the colors associated with the fluorescence of specificcompounds; and

FIG. 33 illustrates an electrosurgical probe having active electrodesrecessed within a plasma chamber at the distal end of the probe.

FIG. 34 illustrates an electrosurgical probe having active electrodesrecessed within a number of interconnected chambers at the distal end ofthe probe.

FIG. 35A-35B illustrate a tissue treatment surface of an electrosurgicalprobe having spacers.

FIG. 36A-36B illustrate an electrosurgical probe having a vent/openingthat assists in the prevention of accumulated heat between the tissuetreatment surface and the tissue being treated.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

In the present invention, high frequency (RF) electrical energy isapplied to one or more active electrodes in the presence of electricallyconductive fluid to remove and/or modify body tissue. The techniques ofthe present invention may be performed in a conventional open surgeryenvironment or in a minimally invasive manner using cannulas or portaccess devices. The present invention is useful in procedures where thetissue site is flooded or submerged with an electrically conductingfluid, such as arthroscopic surgery of the knee, shoulder, ankle, hip,elbow, hand or foot. Specifically, the present invention is useful inthe resection and/or ablation of the meniscus and the synovial tissuewithin a joint during an arthroscopic procedure. In addition, tissueswhich may be treated by the system and method of the present inventioninclude, but are not limited to, prostate tissue and leiomyomas(fibroids) located within the uterus, gingival tissues and mucosaltissues located in the mouth, tumors, scar tissue, myocardial tissue,collagenous tissue within the eye or epidermal and dermal tissues on thesurface of the skin. The present invention is also useful for resectingtissue within accessible sites of the body that are suitable forelectrode loop resection, such as the resection of prostate tissue,leiomyomas (fibroids) located within the uterus and other diseasedtissue within the body.

The present invention is particularly useful for treating tissue in thehead and neck, such as the car, mouth, pharynx, larynx, esophagus, nasalcavity and sinuses. The head and neck procedures may be performedthrough the mouth or nose using speculae or gags, or using endoscopictechniques, such as functional endoscopic sinus surgery (FESS). Theseprocedures may include the removal of swollen tissue,chronically-diseased inflamed and hypertrophic mucus linings, polyps,turbinates and/or neoplasms from the various anatomical sinuses of theskull, the turbinates and nasal passages, in the tonsil, adenoid,epi-glottic and supra-glottic regions, and salivary glands, submucusresection of the nasal septum, excision of diseased tissue and the like.In other procedures, the present invention may be useful for collagenshrinkage, ablation and/or hemostasis in procedures for treating swollentissue (e.g., turbinates) or snoring and obstructive sleep apnea (e.g.,soft palate, such as the uvula, or tongue/pharynx stiffening, andmidline glossectomies), for gross tissue removal, such astonsillectomies, adenoidectomies, tracheal stenosis and vocal cordpolyps and lesions, or for the resection or ablation of facial tumors ortumors within the mouth and pharynx, such as glossectomies,laryngectomies, acoustic neuroma procedures and nasal ablationprocedures. In addition, the present invention is useful for procedureswithin the ear, such as stapedotomies, tympanostomies or the like.

The present invention may also be useful for treating tissue or otherbody structures in the brain or spine. These procedures include tumorremoval, laminectomy/disketomy procedures for treating herniated disks,decompressive laminectomy for stenosis in the lumbosacral and cervicalspine, medial facetectomy, posterior lumbosacral and cervical spinefusions, treatment of scoliosis associated with vertebral disease,foraminotomies to remove the roof of the intervertebral foramina torelieve nerve root compression and anterior cervical and lumbardiskectomies. These procedures may be performed through open procedures,or using minimally invasive techniques, such as thoracoscopy,arthroscopy, laparascopy or the like.

The present invention may also be useful for maintaining patency in bodypassages subject to occlusion by invasive tissue growth. The apparatusand methods of the present invention may be used to open and maintainpatency in virtually any hollow body passage which may be subject toocclusion by invasive cellular growth or invasive solid tumor growth.Suitable hollow body passages include ducts, orifices, lumens, and thelike, with exemplary body passages including the coronary arteries. Thepresent invention is particularly useful for reducing or eliminating theeffects of restenosis in coronary arteries by selectively removingtissue ingrowth in or around intraluminal prostheses or stents anchoredtherein.

The present invention may also be useful for cosmetic and plasticsurgery procedures in the head and neck. For example, the presentinvention is particularly useful for ablation and sculpting of cartilagetissue, such as the cartilage within the nose that is sculpted duringrhinoplasty procedures. The present invention may also be employed forskin tissue removal and/or collagen shrinkage in the epidermis or dermistissue in the head and neck, e.g., the removal of pigmentations,vascular lesions (e.g., leg veins), scars, tattoos, etc., and for othersurgical procedures on the skin, such as tissue rejuvenation, cosmeticeye procedures (blepharoplasties), wrinkle removal, tightening musclesfor facelifts or browlifts, hair removal and/or transplant procedures,etc.

For convenience, the remaining disclosure will be directed specificallyto the treatment of tissue structures within a joint, e.g., arthroscopicsurgery, but it will be appreciated that the system and method can beapplied equally well to procedures involving other tissues of the body,as well as to other procedures including open procedures, intravascularprocedures, interventional cardiology procedures, urology, laparascopy,arthroscopy, thoracoscopy or other cardiac procedures, cosmetic surgery,orthopedics, gynecology, otorhinolaryngology, spinal and neurologicprocedures, oncology and the like.

In one aspect of the invention, the body tissue is volumetricallyremoved or ablated. In this procedure, a high frequency voltagedifference is applied between one or more active electrode(s) and one ormore return electrode(s) to non-thermally develop a high electric fieldintensities in the vicinity of the target tissue. The high electricfield intensities adjacent the active electrode(s) lead to electricfield induced molecular breakdown of target tissue through moleculardissociation (rather than thermal evaporation or carbonization).Applicant believes that the tissue structure is volumetrically removedthrough molecular disintegration of larger organic molecules intosmaller molecules and/or atoms, such as hydrogen, oxygen, oxides ofcarbon, hydrocarbons and nitrogen compounds. This moleculardisintegration completely removes the tissue structure, as opposed todehydrating the tissue material by the removal of liquid within thecells of the tissue, as is typically the case with electrosurgicaldesiccation and vaporization.

The high electric field intensities may be generated by applying a highfrequency voltage that is sufficient to vaporize an electricallyconducting fluid over at least a portion of the active electrode(s) inthe region between the distal tip of the active electrode(s) and thetarget tissue. Preferably, the active electrode(s) are maintained at alow temperature to prevent thermal damage to the surrounding tissue andto improve the ionization of the electrically conductive fluid. Theelectrically conductive fluid may be a liquid or gas, such as isotonicsaline or blood, delivered to the target site, or a viscous fluid, suchas a gel, applied to the target site. Since the vapor layer or vaporizedregion has a relatively high electrical impedance, it increases thevoltage differential between the active electrode tip and the tissue andcauses ionization within the vapor layer due to the presence of anionizable species (e.g., sodium when isotonic saline is the electricallyconducting fluid). This ionization, under the conditions describedherein, induces the discharge of energetic electrons and photons fromthe vapor layer and to the surface of the target tissue. This energy maybe in the form of energetic photons (e.g., ultraviolet radiation),energetic particles (e.g., electrons or ions) or a combination thereof.A more detailed description of this phenomena, termed Coblation® can befound in commonly assigned U.S. Pat. No. 5,697,882 the completedisclosure of which is incorporated herein by reference.

Applicant believes that the principle mechanism of tissue removal in theCoblation® mechanism of the present invention is energetic electrons orions that have been energized in a plasma adjacent to the activeelectrode(s). When a liquid is heated enough that atoms vaporize off thesurface faster than they recondense, a gas is formed. When the gas isheated enough that the atoms collide with each other and knock theirelectrons off in the process, an ionized gas or plasma is formed (theso-called “fourth state of matter”). A more complete description ofplasma can be found in Plasma Physics, by R. J. Goldston and P. H.Rutherford of the Plasma Physics Laboratory of Princeton University(1995). When the density of the vapor layer (or within a bubble formedin the electrically conducting liquid) becomes sufficiently low (i.e.,less than approximately 1020 atoms/cm3 for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Once the ionic particles in the plasmalayer have sufficient energy, they accelerate towards the target tissue.Energy evolved by the energetic electrons (e.g., 3.5 eV to 5 eV) cansubsequently bombard a molecule and break its bonds, dissociating amolecule into free radicals, which then combine into final gaseous orliquid species.

Plasmas may be formed by heating a small of gas and ionizing the gas bydriving an electric current through it, or by shining radio waves intothe gas. Generally, these methods of plasma formation give energy tofree electrons in the plasma directly, and then electron-atom collisionsliberate more electrons, and the process cascades until the desireddegree of ionization is achieved. Often, the electrons carry theelectrical current or absorb the radio waves and, therefore, are hotterthan the ions. Thus, in applicant's invention, the electrons, which arecarried away from the tissue towards the return electrode, carry most ofthe plasma's heat with them, allowing the ions to break apart the tissuemolecules in a substantially non-thermal manner.

In some embodiments, the present invention applies high frequency (RF)electrical energy in an electrically conducting fluid environment toremove (i.e., resect, cut or ablate) a tissue structure and to sealtransected vessels within the region of the target tissue. The presentinvention is particularly useful for sealing larger arterial vessels,e.g., on the order of 1 mm or greater. In some embodiments, a highfrequency power supply is provided having an ablation mode, wherein afirst voltage is applied to an active electrode sufficient to effectmolecular dissociation or disintegration of the tissue, and acoagulation mode, wherein a second, lower voltage is applied to anactive electrode (either the same or a different electrode) sufficientto achieve hemostasis of severed vessels within the tissue. In otherembodiments, an electrosurgical instrument is provided having one ormore coagulation electrode(s) configured for sealing a severed vessel,such as an arterial vessel, and one or more active electrodes configuredfor either contracting the collagen fibers within the tissue or removing(ablating) the tissue, e.g., by applying sufficient energy to the tissueto effect molecular dissociation. In the latter embodiments, thecoagulation electrode(s) may be configured such that a single voltagecan be applied to coagulate with the coagulation electrode(s), and toablate with the active electrode(s). In other embodiments, the powersupply is combined with the coagulation instrument such that thecoagulation electrode is used when the power supply is in thecoagulation mode (low voltage), and the active electrode(s) are usedwhen the power supply is in the ablation mode (higher voltage).

In most embodiments, the present invention comprises platinum orplatinum-iridium electrodes to deliver the high frequency energy to theconductive fluid. The platinum/platinum-iridium electrodes have a lowresistivity and low thermal conductivity so as to minimize theproduction of heat in the electrodes and the electrically conductivefluid. This allows more electrical energy to be applied directly intothe conductive fluid.

In one method of the present invention, one or more active electrodesare brought into close proximity to tissue at a target site, and thepower supply is activated in the ablation mode such that sufficientvoltage is applied between the active electrodes and the returnelectrode to volumetrically remove the tissue through moleculardissociation, as described below. During this process, vessels withinthe tissue will be severed. Smaller vessels will be automatically sealedwith the system and method of the present invention. Larger vessels, andthose with a higher flow rate, such as arterial vessels, may not beautomatically sealed in the ablation mode. In these cases, the severedvessels may be sealed by activating a control (e.g., a foot pedal) toreduce the voltage of the power supply into the coagulation mode. Inthis mode, the active electrodes may be pressed against the severedvessel to provide sealing and/or coagulation of the vessel.Alternatively, a coagulation electrode located on the same or adifferent instrument may be pressed against the severed vessel. Once thevessel is adequately sealed, the surgeon activates a control (e.g.,another foot pedal) to increase the voltage of the power supply backinto the ablation mode.

The present invention is also useful for removing or ablating tissuearound nerves, such as spinal, or cranial nerves, e.g., optic nerve,facial nerves, vestibulocochlear nerves and the like. One of thesignificant drawbacks with the prior art microdebriders and lasers isthat these devices do not differentiate between the target tissue andthe surrounding nerves or bone. Therefore, the surgeon must be extremelycareful during these procedures to avoid damage to the bone or nerveswithin and around the nasal cavity. In the present invention, theCoblation® process for removing tissue results in extremely small depthsof collateral tissue damage as discussed above. This allows the surgeonto remove tissue close to a nerve without causing collateral damage tothe nerve fibers.

In addition to the generally precise nature of the novel mechanisms ofthe present invention, applicant has discovered an additional method ofensuring that adjacent nerves are not damaged during tissue removal.According to the present invention, systems and methods are provided fordistinguishing between the fatty tissue immediately surrounding nervefibers and the normal tissue that is to be removed during the procedure.Nerves usually comprise a connective tissue sheath, or epineurium,enclosing the bundles of nerve fibers, each bundle being surrounded byits own sheath of connective tissue (the perineurium) to protect thesenerve fibers. The outer protective tissue sheath or epineurium typicallycomprises a fatty tissue (e.g., adipose tissue) having substantiallydifferent electrical properties than the normal target tissue, such asthe turbinates, polyps, mucus tissue or the like, that are, for example,removed from the nose during sinus procedures. The system of the presentinvention measures the electrical properties of the tissue at the tip ofthe probe with one or more active electrode(s). These electricalproperties may include electrical conductivity at one, several or arange of frequencies (e.g., in the range from 1 kHz to 100 MHz),dielectric constant, capacitance or combinations of these. In thisembodiment, an audible signal may be produced when the sensingelectrode(s) at the tip of the probe detects the fatty tissuesurrounding a nerve, or direct feedback control can be provided to onlysupply power to the active electrode(s) either individually or to thecomplete array of electrodes, if and when the tissue encountered at thetip or working end of the probe is normal tissue based on the measuredelectrical properties.

In one embodiment, the current limiting elements (discussed in detailabove) are configured such that the active electrodes will shut down orturn off when the electrical impedance reaches a threshold level. Whenthis threshold level is set to the impedance of the fatty tissue 4surrounding nerves 6, the active electrodes will shut off whenever theycome in contact with, or in close proximity to, nerves. Meanwhile, theother active electrodes, which are in contact with or in close proximityto nasal tissue, will continue to conduct electric current to the returnelectrode. This selective ablation or removal of lower impedance tissuein combination with the Coblation® mechanism of the present inventionallows the surgeon to precisely remove tissue around nerves or bone.Applicant has found that the present invention is capable ofvolumetrically removing tissue closely adjacent to nerves withoutimpairment the function of the nerves, and without significantlydamaging the tissue of the epineurium. One of the significant drawbackswith the prior art microdebriders and lasers is that these devices donot differentiate between the target tissue and the surrounding nervesor bone. Therefore, the surgeon must be extremely careful during theseprocedures to avoid damage to the bone or nerves within and around thenasal cavity. In the present invention, the Coblation® process forremoving tissue results in extremely small depths of collateral tissuedamage as discussed above. This allows the surgeon to remove tissueclose to a nerve without causing collateral damage to the nerve fibers.

In addition to the above, applicant has discovered that the Coblation®mechanism of the present invention can be manipulated to ablate orremove certain tissue structures, while having little effect on othertissue structures. As discussed above, the present invention uses atechnique of vaporizing electrically conductive fluid to form a plasmalayer or pocket around the active electrode(s), and then inducing thedischarge of energy from this plasma or vapor layer to break themolecular bonds of the tissue structure. Based on initial experiments,applicants believe that the free electrons within the ionized vaporlayer are accelerated in the high electric fields near the electrodetip(s). When the density of the vapor layer (or within a bubble formedin the electrically conducting liquid) becomes sufficiently low (i.e.,less than approximately 1020 atoms/cm3 for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Energy evolved by the energeticelectrons (e.g., 4 to 5 eV) can subsequently bombard a molecule andbreak its bonds, dissociating a molecule into free radicals, which thencombine into final gaseous or liquid species.

The energy evolved by the energetic electrons may be varied by adjustinga variety of factors, such as: the number of active electrodes;electrode size and spacing; electrode surface area; asperities and sharpedges on the electrode surfaces; electrode materials; applied voltageand power; current limiting means, such as inductors; electricalconductivity of the fluid in contact with the electrodes; density of thefluid; and other factors. Accordingly, these factors can be manipulatedto control the energy level of the excited electrons. Since differenttissue structures have different molecular bonds, the present inventioncan be configured to break the molecular bonds of certain tissue, whilehaving too low an energy to break the molecular bonds of other tissue.For example, fatty tissue, (e.g., adipose) tissue has double bonds thatrequire a substantially higher energy level than 4 to 5 eV to break.Accordingly, the present invention in its current configurationgenerally does not ablate or remove such fatty tissue. Of course,factors may be changed such that these double bonds can also be brokenin a similar fashion as the single bonds (e.g., increasing voltage orchanging the electrode configuration to increase the current density atthe electrode tips). A more complete description of this phenomena canbe found in co-pending U.S. patent application Ser. No. 09/032,375,filed Feb. 27, 1998, the complete disclosure of which is incorporatedherein by reference.

The present invention also provides systems, apparatus and methods forselectively removing tumors, e.g., facial tumors, or other undesirablebody structures while minimizing the spread of viable cells from thetumor. Conventional techniques for removing such tumors generally resultin the production of smoke in the surgical setting, termed anelectrosurgical or laser plume, which can spread intact, viablebacterial or viral particles from the tumor or lesion to the surgicalteam or to other portions of the patient's body. This potential spreadof viable cells or particles has resulted in increased concerns over theproliferation of certain debilitating and fatal diseases, such ashepatitis, herpes, HIV and papillomavirus. In the present invention,high frequency voltage is applied between the active electrode(s) andone or more return electrode(s) to volumetrically remove at least aportion of the tissue cells in the tumor through the dissociation ordisintegration of organic molecules into non-viable atoms and molecules.Specifically, the present invention converts the solid tissue cells intonon-condensable gases that are no longer intact or viable, and thus, notcapable of spreading viable tumor particles to other portions of thepatient's brain or to the surgical staff. The high frequency voltage ispreferably selected to effect controlled removal of these tissue cellswhile minimizing substantial tissue necrosis to surrounding orunderlying tissue. A more complete description of this phenomena can befound in co-pending U.S. patent application 09/109,219, filed Jun. 30,1998, the complete disclosure of which is incorporated herein byreference.

The electrosurgical instrument will comprise a shaft having a proximalend and a distal end which supports one or more active electrode(s). Theshaft may assume a wide variety of configurations, with the primarypurpose being to mechanically support one or more active electrode(s)and permit the treating physician to manipulate the electrode(s) from aproximal end of the shaft. Usually, an electrosurgical probe shaft willbe a narrow-diameter rod or tube, more usually having dimensions whichpermit it to be introduced through a cannula into the patient's body.Thus, the probe shaft will typically have a length of at least 5 cm foropen procedures and at least 10 cm, more typically being 20 cm, orlonger for endoscopic procedures. The probe shaft will typically have adiameter of at least 1 mm and frequently in the range from 1 to 10 mm.For dermatology or other procedures on the skin surface, the shaft willhave any suitable length and diameter that would facilitate handling bythe surgeon.

The electrosurgical instrument may also be a catheter that is deliveredpercutaneously and/or endoluminally into the patient by insertionthrough a conventional or specialized guide catheter, or the inventionmay include a catheter having an active electrode or electrode arrayintegral with its distal end. The catheter shaft may be rigid orflexible, with flexible shafts optionally being combined with agenerally rigid external tube for mechanical support. Flexible shaftsmay be combined with pull wires, shape memory actuators, and other knownmechanisms for effecting selective deflection of the distal end of theshaft to facilitate positioning of the electrode or electrode array. Thecatheter shaft will usually include a plurality of wires or otherconductive elements running axially therethrough to permit connection ofthe electrode or electrode array and the return electrode to a connectorat the proximal end of the catheter shaft. The catheter shaft mayinclude a guide wire for guiding the catheter to the target site, or thecatheter may comprise a steerable guide catheter. The catheter may alsoinclude a substantially rigid distal end portion to increase the torquecontrol of the distal end portion as the catheter is advanced furtherinto the patient's body. Specific shaft designs will be described indetail in connection with the figures hereinafter.

In a specific configuration the electrosurgical instrument comprisesplatinum or platinum-iridium electrodes. Applicant has found that theplatinum/platinum-iridium electrodes provide a superior interface withthe electrically conductive medium so that there is less thermal heatingand a more efficient creation of the plasma layer. Moreover, the lowresistivity and low thermal conductivity of the platinum electrodescause less thermal damage to the surrounding tissue and ablates thetarget tissue in a more efficient manner.

The active electrode(s) are preferably supported within or by aninorganic insulating support positioned near the distal end of theinstrument shaft. The return electrode may be located on the instrumentshaft, on another instrument or on the external surface of the patient(i.e., a dispersive pad). In most applications, applicant has found thatit is preferably to have the return electrode on or near the shaft ofthe instrument to confine the electric currents to the target site. Insome applications and under certain conditions, however, the inventionmay be practiced in a monopolar mode, with the return electrode attachedto the external surface of the patient. Accordingly, the returnelectrode is preferably either integrated with the instrument shaft, oranother instrument located in close proximity to the distal end of theinstrument shaft. The proximal end of the instrument will include theappropriate electrical connections for coupling the return electrode(s)and the active electrode(s) to a high frequency power supply, such as anelectrosurgical generator.

The current flow path between the active electrodes and the returnelectrode(s) may be generated by submerging the tissue site in anelectrical conducting fluid (e.g., within a viscous fluid, such as anelectrically conductive gel) or by directing an electrically conductingfluid along a fluid path to the target site (i.e., a liquid, such asisotonic saline, hypotonic saline or a gas, such as argon). Theconductive gel may also be delivered to the target site to achieve aslower more controlled delivery rate of conductive fluid. In addition,the viscous nature of the gel may allow the surgeon to more easilycontain the gel around the target site (e.g., rather than attempting tocontain isotonic saline). A more complete description of an exemplarymethod of directing electrically conducting fluid between the active andreturn electrodes is described in U.S. Pat. No. 5,697,281, previouslyincorporated herein by reference. Alternatively, the body's naturalconductive fluids, such as blood, may be sufficient to establish aconductive path between the return electrode(s) and the activeelectrode(s), and to provide the conditions for establishing a vaporlayer, as described above. However, conductive fluid that is introducedinto the patient is generally preferred over blood because blood willtend to coagulate at certain temperatures. In addition, the patient'sblood may not have sufficient electrical conductivity to adequately forma plasma in some applications. Advantageously, a liquid electricallyconductive fluid (e.g., isotonic saline) may be used to concurrently“bathe” the target tissue surface to provide an additional means forremoving any tissue, and to cool the region of the target tissue ablatedin the previous moment.

The power supply may include a fluid interlock for interrupting power tothe active electrode(s) when there is insufficient conductive fluidaround the active electrode(s). This ensures that the instrument willnot be activated when conductive fluid is not present, minimizing thetissue damage that may otherwise occur. A more complete description ofsuch a fluid interlock can be found in commonly assigned, co-pendingU.S. patent application Ser. No. 09/058,336, filed Apr. 10, 1998, thecomplete disclosure of which is incorporated herein by reference.

In some procedures, it may also be necessary to retrieve or aspirate theelectrically conductive fluid and/or the non-condensable gaseousproducts of ablation. In addition, it may be desirable to aspirate smallpieces of tissue or other body structures that are not completelydisintegrated by the high frequency energy, or other fluids at thetarget site, such as blood, mucus, the gaseous products of ablation,etc. Accordingly, the system of the present invention may include one ormore suction lumen(s) in the instrument, or on another instrument,coupled to a suitable vacuum source for aspirating fluids from thetarget site. In addition, the invention may include one or moreaspiration electrode(s) coupled to the distal end of the suction lumenfor ablating, or at least reducing the volume of, non-ablated tissuefragments that are aspirated into the lumen. The aspiration electrode(s)function mainly to inhibit clogging of the lumen that may otherwiseoccur as larger tissue fragments are drawn therein. The aspirationelectrode(s) may be different from the ablation active electrode(s), orthe same electrode(s) may serve both functions. A more completedescription of instruments incorporating aspiration electrode(s) can befound in commonly assigned, co-pending patent application entitled“Systems And Methods For Tissue Resection, Ablation And Aspiration”,filed Jan. 21, 1998, the complete disclosure of which is incorporatedherein by reference.

As an alternative or in addition to suction, it may be desirable tocontain the excess electrically conductive fluid, tissue fragmentsand/or gaseous products of ablation at or near the target site with acontainment apparatus, such as a basket, retractable sheath or the like.This embodiment has the advantage of ensuring that the conductive fluid,tissue fragments or ablation products do not flow through the patient'svasculature or into other portions of the body. In addition, it may bedesirable to limit the amount of suction to limit the undesirable effectsuction may have on hemostasis of severed blood vessels.

The present invention may use a single active platinum based electrodeor an array of active platinum based electrodes spaced around the distalsurface of a catheter or probe. In the latter embodiment, the electrodearray usually includes a plurality of independently current-limitedand/or power-controlled active platinum electrodes to apply electricalenergy selectively to the target tissue while limiting the unwantedheating and application of electrical energy to the surrounding tissueand environment resulting from power dissipation into surroundingelectrically conductive fluids, such as blood, normal saline, and thelike. The active electrodes may be independently current-limited byisolating the terminals from each other and connecting each terminal toa separate power source that is isolated from the other activeelectrodes. Alternatively, the active electrodes may be connected toeach other at either the proximal or distal ends of the catheter to forma single wire that couples to a power source.

In one configuration, each individual active electrode in the electrodearray is electrically insulated from all other active electrodes in thearray within said instrument and is connected to a power source which isisolated from each of the other active electrodes in the array or tocircuitry which limits or interrupts current flow to the activeelectrode when low resistivity material (e.g., blood, electricallyconductive saline irrigant or electrically conductive gel) causes alower impedance path between the return electrode and the individualactive electrode. The isolated power sources for each individual activeelectrode may be separate power supply circuits having internalimpedance characteristics which limit power to the associated activeelectrode when a low impedance return path is encountered. By way ofexample, the isolated power source may be a user selectable constantcurrent source. In this embodiment, lower impedance paths willautomatically result in lower resistive heating levels since the heatingis proportional to the square of the operating current times theimpedance. Alternatively, a single power source may be connected to eachof the active electrodes through independently actuatable switches, orby independent current limiting elements, such as inductors, capacitors,resistors and/or combinations thereof. The current limiting elements maybe provided in the instrument, connectors, cable, controller or alongthe conductive path from the controller to the distal tip of theinstrument. Alternatively, the resistance and/or capacitance may occuron the surface of the active electrode(s) due to oxide layers which formselected active electrodes (e.g., titanium or a resistive coating on thesurface of metal, such as platinum).

The tip region of the instrument may comprise many independent activeelectrodes designed to deliver electrical energy in the vicinity of thetip. The selective application of electrical energy to the conductivefluid is achieved by connecting each individual active electrode and thereturn electrode to a power source having independently controlled orcurrent limited channels. The return electrode(s) may comprise a singletubular member of conductive material proximal to the electrode array atthe tip which also serves as a conduit for the supply of theelectrically conducting fluid between the active and return electrodes.Alternatively, the instrument may comprise an array of return electrodesat the distal tip of the instrument (together with the activeelectrodes) to maintain the electric current at the tip. The applicationof high frequency voltage between the return electrode(s) and theelectrode array results in the generation of high electric fieldintensities at the distal tips of the active electrodes with conductionof high frequency current from each individual active electrode to thereturn electrode. The current flow from each individual active electrodeto the return electrode(s) is controlled by either active or passivemeans, or a combination thereof, to deliver electrical energy to thesurrounding conductive fluid while minimizing energy delivery tosurrounding (non-target) tissue.

The application of a high frequency voltage between the return platinumelectrode(s) and the active platinum electrode(s) for appropriate timeintervals effects cutting, removing, ablating, shaping, contracting orotherwise modifying the target tissue. The tissue volume over whichenergy is dissipated (i.e., a high current density exists) may be moreprecisely controlled, for example, by the use of a multiplicity of smallactive platinum electrodes whose effective diameters or principaldimensions range from about 10 mm to 0.01 mm, preferably from about 2 mmto 0.05 mm, and more preferably from about 1 mm to 0.1 mm. Electrodeareas for both circular and non-circular terminals will have a contactarea (per active electrode) below 50 mm² for electrode arrays and aslarge as 75² mm for single electrode embodiments. In multiple electrodearrays, the contact area of each active electrode is typically in therange from 0.0001 mm² to 1 mm², and more preferably from 0.001 mm² to0.5 mm². The circumscribed area of the electrode array or activeelectrode is in the range from 0.25 mm² to 75 mm², preferably from 0.5mm² to 40 mm². In multiple electrode embodiments, the array will usuallyinclude at least two isolated active electrodes, often at least fiveactive electrodes, often greater than 10 active electrodes and even 50or more active electrodes, disposed over the distal contact surfaces onthe shaft. The use of small diameter active electrodes increases theelectric field intensity and reduces the extent or depth of tissueheating as a consequence of the divergence of current flux lines whichemanate from the exposed surface of each active electrode.

The area of the tissue treatment surface can vary widely, and the tissuetreatment surface can assume a variety of geometries, with particularareas and geometries being selected for specific applications. Thegeometries can be planar, concave, convex, hemispherical, conical,linear “in-line” array or virtually any other regular or irregularshape. Most commonly, the active electrode(s) or active electrode(s)will be formed at the distal tip of the electrosurgical instrumentshaft, frequently being planar, disk-shaped, or hemispherical surfacesfor use in reshaping procedures or being linear arrays for use incutting. Alternatively or additionally, the active electrode(s) may beformed on lateral surfaces of the electrosurgical instrument shaft(e.g., in the manner of a spatula), facilitating access to certain bodystructures in endoscopic procedures.

In some embodiments, the electrode support and the fluid outlet may berecessed from an outer surface of the instrument or handpiece to confinethe electrically conductive fluid to the region immediately surroundingthe electrode support. In addition, the shaft may be shaped so as toform a cavity around the electrode support and the fluid outlet. Thishelps to assure that the electrically conductive fluid will remain incontact with the active electrode(s) and the return electrode(s) tomaintain the conductive path therebetween. In addition, this will helpto maintain a vapor layer and subsequent plasma layer between the activeelectrode(s) and the tissue at the treatment site throughout theprocedure, which reduces the thermal damage that might otherwise occurif the vapor layer were extinguished due to a lack of conductive fluid.Provision of the electrically conductive fluid around the target sitealso helps to maintain the tissue temperature at desired levels.

In other embodiments, the active electrodes are spaced from the tissue asufficient distance to minimize or avoid contact between the tissue andthe vapor layer formed around the active electrodes. In theseembodiments, contact between the heated electrons in the vapor layer andthe tissue is minimized as these electrons travel from the vapor layerback through the conductive fluid to the return electrode. The ionswithin the plasma, however, will have sufficient energy, under certainconditions such as higher voltage levels, to accelerate beyond the vaporlayer to the tissue. Thus, the tissue bonds are dissociated or broken asin previous embodiments, while minimizing the electron flow, and thusthe thermal energy, in contact with the tissue.

The electrically conducting fluid should have a threshold conductivityto provide a suitable conductive path between the return electrode andthe active electrode(s). The electrical conductivity of the fluid (inunits of milliSiemans per centimeter or mS/cm) will usually be greaterthan 0.2 mS/cm, preferably will be greater than 2 mS/cm and morepreferably greater than 10 mS/cm. In an exemplary embodiment, theelectrically conductive fluid is isotonic saline, which has aconductivity of about 17 mS/cm. Applicant has found that a moreconductive fluid, or one with a higher ionic concentration, will usuallyprovide a more aggressive ablation rate. For example, a saline solutionwith higher levels of sodium chloride than conventional saline (which ison the order of about 0.9% sodium chloride) e.g., on the order ofgreater than 1% or between about 3% and 20%, may be desirable.Alternatively, the invention may be used with different types ofconductive fluids that increase the power of the plasma layer by, forexample, increasing the quantity of ions in the plasma, or by providingions that have higher energy levels than sodium ions. For example, thepresent invention may be used with elements other than sodium, such aspotassium, magnesium, calcium and other metals near the left end of theperiodic chart. In addition, other electronegative elements may be usedin place of chlorine, such as fluorine.

The voltage difference applied between the return electrode(s) and theactive electrode(s) will be at high or radio frequency, typicallybetween about 5 kHz and 20 MHz, usually being between about 30 kHz and2.5 MHz, preferably being between about 50 kHz and 500 kHz, often lessthan 350 kHz, and often between about 100 kHz and 200 kHz. In someapplications, applicant has found that a frequency of about 100 kHz isuseful because the tissue impedance is much greater at this frequency.In other applications, such as procedures in or around the heart or headand neck, higher frequencies may be desirable (e.g., 400 kHz-600 kHz) tominimize low frequency current flow into the heart or the nerves of thehead and neck. The RMS (root mean square) voltage applied will usuallybe in the range from about 5 volts to 1000 volts, preferably being inthe range from about 10 volts to 500 volts, often between about 150volts to 350 volts depending on the active electrode size, the operatingfrequency and the operation mode of the particular procedure or desiredeffect on the tissue (i.e., contraction, coagulation, cutting orablation). Typically, the peak-to-peak voltage for ablation or cuttingwith a square wave form will be in the range of 10 volts to 2000 voltsand preferably in the range of 100 volts to 1800 volts and morepreferably in the range of about 300 to 1500 volts, often in the rangeof about 300 volts to 800 volts peak to peak (again, depending on theelectrode size, the operating frequency and the operation mode). Lowerpeak-to-peak voltages will be used for tissue coagulation or collagencontraction and will typically be in the range from 50 to 1500,preferably 100 to 1000 and more preferably 120 to 400 volts peak-to-peak(again, these values are computed using a square wave form). Higherpeak-to-peak voltages, e.g., greater than about 700 volts peak-to-peak,may be desirable for ablation of harder material, such as bone,depending on other factors, such as the electrode geometries and thecomposition of the conductive fluid.

As discussed above, the voltage is usually delivered in a series ofvoltage pulses or alternating current of time varying voltage amplitudewith a sufficiently high frequency (e.g., on the order of 5 kHz to 20MHz) such that the voltage is effectively applied continuously (ascompared with e.g., lasers claiming small depths of necrosis, which aregenerally pulsed about 10 Hz to 20 Hz). In addition, the duty cycle(i.e., cumulative time in any one-second interval that energy isapplied) is on the order of about 50% for the present invention, ascompared with pulsed lasers which typically have a duty cycle of about0.0001%.

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being heated, and/or the maximum allowedtemperature selected for the instrument tip. The power source allows theuser to select the voltage level according to the specific requirementsof a particular neurosurgery procedure, cardiac surgery, arthroscopicsurgery, dermatological procedure, ophthalmic procedures, open surgeryor other endoscopic surgery procedure. For cardiac procedures andpotentially for neurosurgery, the power source may have an additionalfilter, for filtering leakage voltages at frequencies below 100 kHz,particularly voltages around 60 kHz. Alternatively, a power sourcehaving a higher operating frequency, e.g., 300 to 600 kHz may be used incertain procedures in which stray low frequency currents may beproblematic. A description of one suitable power source can be found inco-pending Patent Applications 09/058,571 and 09/058,336, filed Apr. 10,1998, the complete disclosure of both applications are incorporatedherein by reference for all purposes.

The power source may be current limited or otherwise controlled so thatundesired heating of the target tissue or surrounding (non-target)tissue does not occur. In a presently preferred embodiment of thepresent invention, current limiting inductors are placed in series witheach independent active electrode, where the inductance of the inductoris in the range of 10 uH to 50,000 uH, depending on the electricalproperties of the target tissue, the desired tissue heating rate and theoperating frequency. Alternatively, capacitor-inductor (LC) circuitstructures may be employed, as described previously in U.S. Pat. No.5,697,909, the complete disclosure of which is incorporated herein byreference. Additionally, current limiting resistors may be selected.Preferably, these resistors will have a large positive temperaturecoefficient of resistance so that, as the current level begins to risefor any individual active electrode in contact with a low resistancemedium (e.g., saline irrigant or blood), the resistance of the currentlimiting resistor increases significantly, thereby minimizing the powerdelivery from said active electrode into the low resistance medium(e.g., saline irrigant or blood).

It should be clearly understood that the invention is not limited toelectrically isolated active platinum electrodes, or even to a pluralityof active platinum electrodes. For example, the array of active platinumelectrodes may be connected to a single lead that extends through thecatheter shaft to a power source of high frequency current.Alternatively, the instrument may incorporate a single electrode thatextends directly through the catheter shaft or is connected to a singlelead that extends to the power source. The active electrode(s) may haveball shapes (e.g., for tissue vaporization and desiccation), twizzleshapes (for vaporization and needle-like cutting), spring shapes (forrapid tissue debulking and desiccation), twisted metal shapes, annularor solid tube shapes or the like. Alternatively, the electrode(s) maycomprise a plurality of filaments, rigid or flexible brush electrode(s)(for debulking a tumor, such as a fibroid, bladder tumor or a prostateadenoma), side-effect brush electrode(s) on a lateral surface of theshaft, coiled electrode(s) or the like.

In one embodiment, an electrosurgical catheter or probe comprises asingle active platinum electrode that extends from an insulating member,e.g., ceramic, at the distal end of the shaft. The insulating member ispreferably a tubular structure that separates the active platinumelectrode from a tubular or annular return platinum electrode positionedproximal to the insulating member and the active platinum electrode. Inanother embodiment, the catheter or probe includes a single activeplatinum electrode that can be rotated relative to the rest of thecatheter body, or the entire catheter may be rotated related to thelead. The single active platinum electrode can be positioned adjacentthe abnormal tissue and energized and rotated as appropriate to removethis tissue.

The current flow path between the active platinum electrode(s) and thereturn platinum electrode(s) may be generated by submerging the tissuesite in an electrical conducting fluid (e.g., within a viscous fluid,such as an electrically conductive gel) or by directing an electricallyconducting fluid along a fluid path to the target site (i.e., a liquid,such as isotonic saline, or a gas, such as argon). This latter method isparticularly effective in a dry environment (i.e., the tissue is notsubmerged in fluid) because the electrically conducting fluid provides asuitable current flow path from the active electrode to the returnelectrode.

Referring to FIG. 1, an exemplary electrosurgical system 5 for treatmentof tissue in the body will now be described in detail. Electrosurgicalsystem 5 is generally useful for minimally invasive procedures withinthe body, wherein a surgical instrument is introduced through apercutaneous penetration, or through a natural opening in the patient.As shown, electrosurgical system 5 generally includes an electrosurgicalprobe 20 connected to a power supply 10 for providing high frequencyvoltage to one or more active electrodes 42 on probe 20. Probe 20includes a connector housing 44 at its proximal end, which can beremovably connected to a probe receptacle 32 of a probe cable 22. Theproximal portion of cable 22 has a connector 34 to couple probe 20 topower supply 10. Power supply 10 has an operator controllable voltagelevel adjustment 38 to change the applied voltage level, which isobservable at a voltage level display 40. Power supply 10 also includesone or more foot pedal(s) 24 and one or more cable(s) 26 which are eachremovably coupled to receptacle 30 with a cable connector 28. The footpedal(s) 24 may include a second pedal (not shown) for remotelyadjusting the energy level applied to active electrodes 104, and a thirdpedal (also not shown) for switching between an ablation mode and asub-ablation mode (such as coagulation or contraction).

In an exemplary embodiment, a first foot pedal 24 is used to place thepower supply into the “ablation” mode and second foot pedal (not shown)places power supply 28 into the “coagulation” mode. The third foot pedal(not shown) allows the user to adjust the voltage level within the“ablation” mode. In the ablation mode, a sufficient voltage is appliedto the active electrodes to establish the requisite conditions formolecular dissociation of the tissue (i.e., forming a plasma withsufficient energy to ablate tissue). As discussed above, the requisitevoltage level for ablation will vary depending on the number, size,shape and spacing of the electrodes, the distance in which theelectrodes extend from the support member, etc. When the surgeon isusing the power supply in the “ablation” mode, voltage level adjustment40 or third foot pedal may be used to adjust the voltage level to adjustthe degree or aggressiveness of the ablation. Of course, it will berecognized that the voltage and modality of the power supply may becontrolled by other input devices. However, applicant has found thatfoot pedals are convenient methods of controlling the power supply whilemanipulating the probe during a surgical procedure.

In the coagulation mode, the power supply 28 applies a low enoughvoltage to one or more active electrodes (or one or more coagulationelectrodes) to avoid vaporization of the electrically conductive fluid,formation of a plasma and subsequent molecular dissociation of thetissue. The surgeon may automatically toggle the power supply betweenthe ablation and coagulation modes by alternatively stepping on theappropriate foot pedals. This allows the surgeon to quickly move betweencoagulation and ablation in situ, without having to remove his/herconcentration from the surgical field or without having to request anassistant to switch the power supply. By way of example, as the surgeonis sculpting soft tissue in the ablation mode, the probe typically willsimultaneously seal and/or coagulate small severed vessels within thetissue. However, larger vessels, or vessels with high fluid pressures(e.g., arterial vessels) may not be sealed in the ablation mode.Accordingly, the surgeon can simply step on the appropriate foot pedal,automatically lowering the voltage level below the threshold level forablation, and apply sufficient pressure onto the severed vessel for asufficient period of time to seal and/or coagulate the vessel. Afterthis is completed, the surgeon may quickly move back into the ablationmode by stepping on the appropriate foot pedal A specific design of asuitable power supply for use with the present invention can be found inU.S. patent application Ser. No. 09/058,571, filed Apr. 10, 1998,previously incorporated herein by reference.

Referring now to FIGS. 2 and 3, a representative high frequency powersupply for use according to the principles of the present invention willnow be described. The high frequency power supply of the presentinvention is configured to apply a high frequency voltage of about 10 to500 volts RMS between one or more active electrodes (and/or coagulationelectrode) and one or more return electrodes. In the exemplaryembodiment, the power supply applies about 70-350 volts RMS in theablation mode and about 20 to 90 volts in a subablation mode, preferably45 to 70 volts in coagulation mode (these values will, of course, varydepending on the probe configuration attached to the power supply andthe desired mode of operation).

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being heated, and/or the maximum allowedtemperature selected for the probe tip. The power source allows the userto select the voltage level according to the specific requirements of aparticular procedure, e.g., arthroscopic surgery, dermatologicalprocedure, ophthalmic procedures, open surgery or other endoscopicsurgery procedure.

As shown in FIG. 2, the power supply generally comprises a radiofrequency (RF) power oscillator 100 having output connections forcoupling via a power output signal 102 to the load impedance, which isrepresented by the electrode assembly when the electrosurgical probe isin use. In the representative embodiment, the RF oscillator operates atabout 100 kHz. The RF oscillator is not limited to this frequency andmay operate at frequencies of about 300 kHz to 600 kHz. In particular,for cardiac applications, the RF oscillator will preferably operate inthe range of about 400 kHz to about 600 kHz. The RF oscillator willgenerally supply a square wave signal with a crest factor of about 1 to2. Of course, this signal may be a sine wave signal or other suitablewave signal depending on the application and other factors, such as thevoltage applied, the number and geometry of the electrodes, etc. Thepower output signal 102 is designed to incur minimal voltage decrease(i.e., sag) under load. This improves the applied voltage to the activeelectrodes and the return electrode, which improves the rate ofvolumetric removal (ablation) of tissue.

Power is supplied to the oscillator 100 by a switching power supply 104coupled between the power line and the RF oscillator rather than aconventional transformer. The switching power supply 140 allows thegenerator to achieve high peak power output without the large size andweight of a bulky transformer. The architecture of the switching powersupply also has been designed to reduce electromagnetic noise such thatU.S. and foreign EMI requirements are met. This architecture comprises azero voltage switching or crossing, which causes the transistors to turnON and OFF when the voltage is zero. Therefore, the electromagneticnoise produced by the transistors switching is vastly reduced. In anexemplary embodiment, the switching power supply 104 operates at about100 kHz.

A controller 106 coupled to the operator controls 105 (i.e., foot pedalsand voltage selector) and display 116, is connected to a control inputof the switching power supply 104 for adjusting the generator outputpower by supply voltage variation. The controller 106 may be amicroprocessor or an integrated circuit. The power supply may alsoinclude one or more current sensors 112 for detecting the outputcurrent. The power supply is preferably housed within a metal casingwhich provides a durable enclosure for the electrical componentstherein. In addition, the metal casing reduces the electromagnetic noisegenerated within the power supply because the grounded metal casingfunctions as a “Faraday shield”, thereby shielding the enviromnent frominternal sources of electromagnetic noise.

The power supply generally comprises a main or mother board containinggeneric electrical components required for many different surgicalprocedures (e.g., arthroscopy, urology, general surgery, dermatology,neurosurgery, etc.), and a daughter board containing applicationspecific current-limiting circuitry (e.g., inductors, resistors,capacitors and the like). The daughter board is coupled to the motherboard by a detachable multi-pin connector to allow convenient conversionof the power supply to, e.g., applications requiring a different currentlimiting circuit design. For arthroscopy, for example, the daughterboard preferably comprises a plurality of inductors of about 200 to 400microhenries, usually about 300 microhenries, for each of the channelssupplying current to the active electrodes (see FIG. 4).

Alternatively, in one embodiment, current limiting inductors are placedin series with each independent active electrode, where the inductanceof the inductor is in the range of 10 uH to 50,000 uH, depending on theelectrical properties of the target tissue, the desired tissue heatingrate and the operating frequency. Alternatively, capacitor-inductor (LC)circuit structures may be employed, as described previously inco-pending PCT application No. PCT/US94/05168, the complete disclosureof which is incorporated herein by reference. Additionally, currentlimiting resistors may be selected. Preferably, these resistors willhave a large positive temperature coefficient of resistance so that, asthe current level begins to rise for any individual active electrode incontact with a low resistance medium (e.g., saline irrigant orconductive gel), the resistance of the current limiting resistorincreases significantly, thereby minimizing the power delivery from saidactive electrode into the low resistance medium (e.g., saline irrigantor conductive gel).

Power output signal may also be coupled to a plurality of currentlimiting elements 96, which are preferably located on the daughter boardsince the current limiting elements may vary depending on theapplication. FIG. 4 illustrates an arrangement that may be used inarthroscopic procedures with a multi-electrode probe. As shown, a highfrequency power supply 28 comprises a voltage source 98 which isconnected to a multiplicity of current limiting elements 96 a, 96 b, . .. 96 z, typically being inductors having an inductance in the range ofabout 100 to 5000 microhenries, with the particular value depending onthe active electrode dimensions, the desired ablation rates, and thelike. Capacitors having capacitance values in the range of about 200 to10,000 picofarads may also be used as the current limiting elements. Itwould also be possible to use resistors as current limiting elements.The current limiting elements any also be part of a resonant circuitstructure, as described in detail in PCT/US94/05168, previouslyincorporated herein by reference.

FIGS. 4-6 illustrate an exemplary electrosurgical probe 20 constructedaccording to the principles of the present invention. As shown in FIG.4, probe 20 generally includes an elongated shaft 100 which may beflexible or rigid, a handle 204 coupled to the proximal end of shaft 100and an electrode support member 102 coupled to the distal end of shaft100. Shaft 100 preferably comprises an electrically conducting material,usually a metal, such as tungsten, stainless steel alloys, platinum orits alloys, titanium or its alloys, molybdenum or its alloys, and nickelor its alloys. Shaft 100 includes an electrically insulating jacket 108,which is typically formed as one or more electrically insulating sheathsor coatings, such as polytetrafluoroethylene, polyimide, and the like.The provision of the electrically insulating jacket over the shaftprevents direct electrical contact between these metal elements and anyadjacent body structure or the surgeon. Such direct electrical contactbetween a body structure (e.g., tendon) and an exposed electrode couldresult in unwanted heating and necrosis of the structure at the point ofcontact causing necrosis.

Handle 204 typically comprises a plastic material that is easily moldedinto a suitable shape for handling by the surgeon. As shown in FIG. 9,handle 204 defines an inner cavity 208 that houses the electricalconnections 250 (discussed below), and provides a suitable interface forconnection to an electrical connecting cable 22 (see FIG. 1). As shownin FIG. 7, the probe will typically include a coding resistor 260 havinga value selected to program different output ranges and modes ofoperation for the power supply. This allows a single power supply to beused with a variety of different probes in different applications (e.g.,dermatology, cardiac surgery, neurosurgery, arthroscopy, etc).

In some embodiments, the probe 20 further includes an identificationelement that is characteristic of the particular electrode assembly sothat the same power supply 28 can be used for different electrosurgicaloperations. In one embodiment, for example, the probe 20 includes avoltage reduction element or a voltage reduction circuit for reducingthe voltage applied between the active electrodes 104 and the returnelectrode 112. The voltage reduction element serves to reduce thevoltage applied by the power supply so that the voltage between theactive electrodes and the return electrode is low enough to avoidexcessive power dissipation into the electrically conducting mediumand/or ablation of the tissue at the target site. The voltage reductionelement primarily allows the electrosurgical probe 20 to be compatiblewith other ArthroCare generators that are adapted to apply highervoltages for ablation or vaporization of tissue. For contraction oftissue, for example, the voltage reduction element will serve to reducea voltage of about 100 to 135 volts rms (which is a setting of 1 on theArthroCare Models 970, 980 and 2000 Generators) to about 45 to 60 voltsrms, which is a suitable voltage for contraction of tissue withoutablation (e.g., molecular dissociation) of the tissue.

Of course, for some procedures, the probe will typically not require avoltage reduction element. Alternatively, the probe may include avoltage increasing element or circuit, if desired.

In the embodiment shown in FIGS. 4-6, an electrode support member 102extends from the distal end of shaft 100 (usually about 1 to 20 mm), andprovides support for a plurality of electrically isolated activeelectrodes 120. Electrode support member 102 and active electrodes 120are preferably secured to a tubular support member 122 within shaft 100by adhesive 124. The active electrodes 120 may be constructed usinground, square, rectangular or other shaped conductive metals. In apreferred embodiment, the active electrodes comprise platinum. In someembodiments, the active electrodes further include between 1% and 30%iridium, and preferably between 5% and 15% iridium. Applicants havefound that the active platinum electrode and the return platinumelectrode(s) produce minimal heat and provide a superior interface forionizing the conductive fluid and non-thermally creating the plasma. Inalternative embodiments, the active electrode materials may also beselected from the group including stainless steel, tungsten and itsalloys, molybdenum and its alloys, titanium and its alloys, nickel-basedalloys, as well as other platinum alloys. Electrode support member 102is preferably a ceramic, glass or glass/ceramic composition (e.g.,aluminum oxide, titanium nitride or the like). Alternatively, electrodesupport member 620 may include the use of high-temperature biocompatibleplastics such as polyether-ether-keytone (PEEK) manufactured by VitrexInternational Products, Inc. or polysulfone manufactured by GE Plastics.The adhesive 620 may, by way of example, be an epoxy (e.g., Master BondEP42HT manufactured by Master Bond) or a silicone-based adhesive.

FIG. 6 illustrates one embodiment of the working end of probe 20. Asshown, a total of 7 circular active platinum electrodes or activeplatinum electrodes 120 are shown in a symmetrical pattern having anactive electrode diameter, D1 in the range from 0.05 mm to 1.5 mm, morepreferably in the range from 0.1 mm to 0.75 mm. The interelectrodespacings, W1 and W2 are preferably in the range from 0.1 mm to 1.5 mmand more preferably in the range from 0.2 mm to 0.75 mm. The distancebetween the outer perimeter of the active electrode 120 and theperimeter of the electrode support member, W3 is preferably in the rangefrom 0.1 mm to 1.5 mm and more preferably in the range from 0.2 mm to0.75 mm. The overall diameter, D2 of the working end of probe 20 ispreferably in the range from 0.5 mm to 10 mm and more preferably in therange from 0.5 mm to 5 mm. As discussed above, the shape of the activeelectrodes may be round, square, triangular, hexagonal, rectangular,tubular, flat strip and the like and may be arranged in a circularlysymmetric pattern as shown in FIG. 6 or may, by way of example, bearranged in a rectangular, square, linear pattern, or the like.

In this embodiment, probe 20 includes a tubular cannula 122 extendingalong shaft 100 radially outward from support member 102 and activeelectrodes 120. The material for cannula 122 may be selected from agroup of electrically conductive metals so that the cannula 122functions as both a structural support member for the array of activeelectrodes 120 as well as a return electrode 112. The support member 122is connected to an electrical lead wire (not shown) at its proximal endwithin a connector housing (not shown) and continues via a suitableconnector to power supply 28 to provide electrical continuity betweenone output pole of high frequency generator 28 and said return electrode112. The cannula 122 may be selected from the group including stainlesssteel, copper-based alloys, titanium or its alloys, and nickel-basedalloys. The thickness of the cannula 122 is preferably in the range from0.08 mm to 1.0 mm and more preferably in the range from 0.05 mm to 0.4mm.

As shown in FIGS. 5 and 6, cannula 122 is covered with an electricallyinsulating sleeve 108 to protect the patient's body from the electriccurrent. Electrically insulating sleeve 108 may be a coating (e.g.,nylon) or heat shrinkable plastic (e.g., fluropolymer or polyester). Asshown in FIG. 5, the proximal portion of the cannula 122 is left exposedto ftunction as the return electrode 112. The length of the returnelectrode 112, L5 is preferably in the range from 1 mm to 30 mm and morepreferably in the range from 2 mm to 20 mm. The spacing between the mostdistal portion of the return electrode 112 and the plane of the tissuetreatment surface of the electrode support member 120, L1 is preferablyin the range from 0.5 mm to 30 mm and more preferably in the range from1 mm to 20 mm. The thickness of the electrically insulating sleeve 108is preferably in the range from 0.01 mm to 0.5 mm and more preferably inthe range from 0.02 mm to 0.2 Mm.

In the embodiment shown in FIGS. 4-6, the electrically conducting fluidis delivered from a fluid delivery element (not shown) that is separatefrom probe 20. In arthroscopic surgery, for example, the body cavitywill be flooded with isotonic saline and the probe 20 will be introducedinto this flooded cavity. Electrically conducting fluid will becontinually resupplied to maintain the conduction path between returnelectrode 112 and active electrodes 102.

FIGS. 7-10 illustrate another embodiment of the present inventionincorporating an aspiration lumen and a loop electrode designed toablate tissue fragments as they as aspirated into the lumen. As shown inFIG. 7, electrosurgical probe 20 includes an elongated shaft 100 whichmay be flexible or rigid, a handle 204 coupled to the proximal end ofshaft 100 and an electrode support member 102 coupled to the distal endof shaft 100. As shown in FIG. 8, probe 20 includes an active loopelectrode 203 and a return electrode 212 spaced proximally from activeloop electrode 203. The probe 200 further includes a suction lumen 220for aspirating excess fluids, bubbles, tissue fragments, and/or productsof ablation from the target site. As shown in FIGS. 7 and 8, suctionlumen 220 extends through support member 102 to a distal opening 222,and extends through shaft 201 and handle 204 to an external connector224 for coupling to a vacuum source. Typically, the vacuum source is astandard hospital pump that provides suction pressure to connector 224and lumen 220.

Electrode support member 102 extends from the distal end of shaft 201usually about 1 to 20 mm), and provides support for loop electrode 203and a ring electrode 204 (see FIG. 22). As shown in FIG. 20, loopelectrode 203 has first and second ends extending from the electrodesupport member 102. The first and second ends are each coupled to, orintegral with, one or more connectors, e.g., wires (not shown), thatextend through the shaft of the probe to its proximal end for couplingto the high frequency power supply. The loop electrode usually extendsabout 0.5 to about 10 mm from the distal end of support member,preferably about 1 to 2 mm. Loop electrode 203 usually extends furtheraway from the support member than the ring electrode 204 to facilitateablation of tissue. As discussed below, loop electrode 203 is especiallyconfigured for tissue ablation, while the ring electrode 204 ablatestissue fragments that are aspirated into suction lumen 220.

Referring to FIG. 10, ring electrode 204 preferably comprises a tungstenor titanium wire having two ends 230, 232 coupled to electricalconnectors (not shown) within support member 102. The wire is bent toform one-half of a figure eight, thereby form a ring positioned overopening 222 of suction lumen 220. This ring inhibits passage of tissuefragments large enough to clog suction lumen 220. Moreover, voltageapplied between ring electrode 204 and return electrode 212 providesufficient energy to ablate these tissue fragments into smallerfragments that are then aspirated through lumen 220. In the presentlypreferred embodiment, ring electrode 204 and loop electrode 203 areelectrically isolated from each other. However, these electrodes 204,203 may be electrically coupled in some applications.

FIGS. 11-17 illustrate another embodiment of the present inventionincluding an electrosurgical probe 300 incorporating an active screenelectrode 302. As shown in FIG. 1, probe 300 includes an elongated shaft304 which may be flexible or rigid, a handle 306 coupled to the proximalend of shaft 304 and an electrode support member 308 coupled to thedistal end of shaft 304. Probe 300 further includes an active screenelectrode 302 and a return electrode 310 spaced proximally from activescreen electrode 302. In this embodiment, active screen electrode 302and support member 308 are configured such that the active electrode 302is positioned on a lateral side of the shaft 304 (e.g., 90 degrees fromthe shaft axis) to allow the physician to access tissue that is offsetfrom the axis of the portal or arthroscopic opening into the jointcavity in which the shaft 304 passes during the procedure. To accomplishthis, probe 300 includes an electrically insulating cap 320 coupled tothe distal end of shaft 304 and having a lateral opening 322 forreceiving support member 308 and screen electrode 302.

The probe 300 further includes a suction connection tube 314 forcoupling to a source of vacuum, and an inner suction lumen 312 (FIG. 12)for aspirating excess fluids, tissue fragments, and/or products ofablation (e.g., bubbles) from the target site. In addition, suctionlumen 312 allows the surgeon to draw loose tissue, e.g., synovialtissue, towards the screen electrode 302, as discussed above. Typically,the vacuum source is a standard hospital pump that provides suctionpressure to connection tube 314 and lumen 312. However, a pump may alsobe incorporated into the high frequency power supply. As shown in FIGS.12, 13 and 16, internal suction lumen 312, which preferably comprisespeek tubing, extends from connection tube 314 in handle 306, throughshaft 304 to an axial opening 316 in support member 308, through supportmember 308 to a lateral opening 318. Lateral opening 318 contacts screenelectrode 302, which includes a plurality of holes 324 (FIG. 214 forallowing aspiration therethrough, as discussed below.

As shown in FIG. 12, handle 306 defines an inner cavity 326 that housesthe electrical connections 328 (discussed above), and provides asuitable interface for connection to an electrical connecting cable 22(see FIG. 1). As shown in FIG. 15, the probe will also include a codingresistor 330 having a value selected to program different output rangesand modes of operation for the power supply. This allows a single powersupply to be used with a variety of different probes in differentapplications (e.g., dermatology, cardiac surgery, neurosurgery,arthroscopy, etc).

Referring to FIG. 16, electrode support member 308 preferably comprisesan inorganic material, such as glass, ceramic, silicon nitride, aluminaor the like, that has been formed with lateral and axial openings 318,316 for suction, and with one or more smaller holes 330 for receivingelectrical connectors 332. In the representative embodiment, supportmember 308 has a cylindrical shape for supporting a circular screenelectrode 302. Of course, screen electrode 302 may have a variety ofdifferent shapes, such as the rectangular shape shown in FIG. 17, whichmay change the associated shape of support member 308. As shown in FIG.13, electrical connectors 332 extend from connections 328, through shaft304 and holes 330 in support member 308 to screen electrode 302 tocouple the active electrode 302 to a high frequency power supply. In therepresentative embodiment, screen electrode 302 is mounted to supportmember 308 by ball wires 334 that extend through holes 336 in screenelectrode 302 and holes 330 in support member 308. Ball wires 334function to electrically couple the screen 302 to connectors 332 and tosecure the screen 302 onto the support member 308. Of course, a varietyof other methods may be used to accomplish these functions, such asnailhead wires, adhesive and standard wires, a channel in the supportmember, etc.

The screen electrode will preferably comprise platinum or aplatinum-iridium alloy. Alternatively, the screen electrode 302 willcomprise a conductive material, such as

tungsten, titanium, molybdenum, stainless steel, aluminum, gold, copperor the like. In some embodiments, it may be advantageous to constructthe active and return electrodes of the same material to eliminate thepossibility of DC currents being created by dissimilar metal electrodes.Screen electrode 302 will usually have a diameter in the range of about0.5 to 8 mm, preferably about 1 to 4 mm, and a thickness of about 0.05to about 2.5 mm, preferably about 0.1 to 1 mm. Electrode 302 willcomprise a plurality of holes 324 having sizes that may vary dependingon the particular application and the number of holes (usually from oneto 50 holes, and preferably about 3 to 20 holes). Holes 324 willtypically be large enough to allow ablated tissue fragments to passthrough into suction lumen 312, typically being about 2 to 30 mils indiameter, preferably about 5 to 20 mils in diameter. In someapplications, it may be desirable to only aspirate fluid and the gaseousproducts of ablation (e.g., bubbles) so that the holes may be muchsmaller, e.g., on the order of less than 10 mils, often less than 5mils.

In the representative embodiment, probe 300 is manufactured as follows:screen electrode 302 is placed on support member 308 so that holes 324are lined up with holes 330. One or more ball wires 334 are insertedthrough these holes, and a small amount of adhesive (e.g., epotek) isplaced around the outer face of support member 308. The ball wires 334are then pulled until screen 302 is flush with support member 308, andthe entire sub-assembly is cured in an oven or other suitable heatingmechanism. The electrode-support member sub-assembly is then insertedthrough the lateral opening in cap 320 and adhesive is applied to thepeek tubing suction lumen 312. The suction lumen 312 is then placedthrough axial hole 316 in support member 308 and this sub-assembly iscured. The return electrode 310 (which is typically the exposed portionof shaft 304) is then adhered to cap 320.

FIGS. 18 and 19 illustrate use of one of the probes 350 of the presentinvention for ablating tissue. As shown, the distal portion of probe 350is introduced to the target site (either endoscopically, through an openprocedure, or directly onto the patient's skin) and active electrode(s)352 are positioned adjacent tissue (FIG. 19 illustrates a probe having asingle active electrode 352, while FIG. 18 illustrates multiple activeelectrodes 352). In the embodiment, the target site is immersed inelectrically conductive fluid, such that the conductive fluid generatesa current flow path (see current flux lines 358) between returnelectrode 356 and the active electrode(s) 352, and the zone between thetissue 354 and electrode support 380 is constantly immersed in thefluid. The power supply (not shown) is then turned on and adjusted suchthat a high frequency voltage difference is applied between activeelectrode(s) 352 and return electrode 356.

In the representative embodiment, the high frequency voltage issufficient to non-thermally convert the electrically conductive fluidbetween the target tissue 354 and active electrode(s) 352 into anionized vapor layer or plasma 360. As a result of the applied voltagedifference between active electrode(s) 352 and the target tissue 354(i.e., the voltage gradient across the plasma layer 360, chargedparticles in the plasma (viz., electrons) are accelerated towards thetissue. At sufficiently high voltage differences, these chargedparticles gain sufficient energy to non-thermally cause dissociation ofthe molecular bonds within tissue structures. This moleculardissociation is accompanied by the volumetric removal (i.e., ablativesublimation) of tissue and the production of low molecular weight gases366, such as oxygen, nitrogen, carbon dioxide, hydrogen and methane. Theshort range of the accelerated charged particles within the tissueconfines the molecular dissociation process to the surface layer 364 tominimize damage and necrosis to the underlying tissue 368.

Referring now to FIG. 20, an exemplary electrosurgical system 411 fortreatment of tissue in ‘dry fields’ will now be described in detail. Ofcourse, system 411 may also be used in ‘wet field’, i.e., the targetsite is immersed in electrically conductive fluid. However, this systemis particularly useful in ‘dry fields’ where the fluid is preferablydelivered through electrosurgical probe to the target site. As shown,electrosurgical system 411 generally comprises an electrosurgicalhandpiece or probe 410 connected to a power supply 428 for providinghigh frequency voltage to a target site and a fluid source 421 forsupplying electrically conducting fluid 450 to probe 410. In addition,electrosurgical system 411 may include an endoscope (not shown) with afiber optic head light for viewing the surgical site, particularly insinus procedures or procedures in the ear or the back of the mouth. Theendoscope may be integral with probe 410, or it may be part of aseparate instrument. The system 411 may also include a vacuum source(not shown) for coupling to a suction lumen or tube 460 (see FIG. 21) inthe probe 410 for aspirating the target site.

As shown, probe 410 generally includes a proximal handle 419 and anelongate shaft 418 having an array 412 of active electrodes 458 at itsdistal end. A connecting cable 434 has a connector 426 for electricallycoupling the active electrodes 458 to power supply 428. The activeelectrodes 458 are electrically isolated from each other and each of theterminals 458 is connected to an active or passive control networkwithin power supply 428 by means of a plurality of individuallyinsulated conductors (not shown). A fluid supply tube 415 is connectedto a fluid tube 414 of probe 410 for supplying electrically conductingfluid 450 to the target site.

FIGS. 21 and 22 illustrate an exemplary embodiment of an electrosurgicalprobe 410 for use with the system 411 of FIG. 20. As shown, the probe410 includes a shaft 100, a proximal handle 404, a distal support member468 and a platinum electrode assembly including a platinum returnelectrode 462 proximally spaced from one or more active platinumelectrodes 464. Similar to previous embodiments, the return electrode462 is not directly connected to active electrodes 464. To complete thiscurrent path so that active electrodes 464 are electrically connected toreturn electrode 462, electrically conducting fluid (e.g., isotonicsaline) is caused to flow therebetween. In the representativeembodiment, probe 410 includes a fluid connector 435 for coupling afluid tube 433 to a source of electrically conductive fluid, such as apump or a gravity driven fluid source. The electrically conducting fluidis delivered through fluid tube 433 to opening 437, as described above.Electrically conducting fluid will be continually resupplied to maintainthe conduction path between return electrode 462 and active electrodes464.

In the representative embodiment, fluid tube 433 comprises peek tubingor a similar type of tubing material. In alternative embodiments, thefluid path may be formed in probe 410 by, for example, an inner lumen oran annular gap between the return electrode 462 and a tubular supportmember within shaft 100 (see FIG. 22). This annular gap may be formednear the perimeter of the shaft 100 such that the electricallyconducting fluid tends to flow radially inward towards the target site,or it may be formed towards the center of shaft 100 so that the fluidflows radially outward. In both of these embodiments, a fluid source(e.g., a bag of fluid elevated above the surgical site or suitablepumping device), is coupled to probe 410 via a fluid supply tube (notshown) that may or may not have a controllable valve.

Referring to FIG. 22, the electrically isolated active electrodes 464are spaced apart over tissue treatment surface 470 of electrode supportmember 468. The tissue treatment surface and individual activeelectrodes 464 will usually have dimensions within the ranges set forthabove. In the representative embodiment, the tissue treatment surface470 has a circular cross-sectional shape with a diameter in the range ofabout 1 mm to 20 mm. The individual active electrodes 464 preferablyextend outward from tissue treatment surface 474 by a distance of about0.0 to 4 mm, usually about 0.2 to 2 mm. Applicant has found that thisconfiguration increases the high electric field intensities andassociated current densities around active electrodes 464 to facilitatethe ablation of tissue as described in detail above. Of course, in otherembodiments, the active electrodes 464 may be flush with tissuetreatment surface 474, be recessed from treatment surface 474, or extendfurther outward than 2 mm, depending on the desired treatment outcome.

In the embodiment of FIG. 22, the probe includes a single, largeropening 409 in the center of tissue treatment surface 470, and aplurality of active electrodes (e.g., about 3 to 15 active electrodes)around the perimeter of surface 470. Alternatively, the probe mayinclude a single, annular, or partially annular, active electrode at theperimeter of the tissue treatment surface. The central opening 409 iscoupled to a suction lumen 425 within shaft 100 and a suction tube 461(FIG. 21) for aspirating tissue, fluids, and/or gases from the targetsite. In this embodiment, the electrically conductive fluid generallyflows radially inward past active electrodes 464 and then back throughthe opening 209. Aspirating the electrically conductive fluid duringsurgery allows the surgeon to see the target site, and it prevents thedispersal of gases, bone tissue fragments and/or calcified deposits intothe patient's body.

In some embodiments, the probe 410 will also include one or moreaspiration electrode(s) (not shown) coupled to the aspiration lumen 425for inhibiting clogging during aspiration of tissue fragments from thesurgical site. A more complete description of these embodiments can befound in commonly assigned co-pending Application Ser. No. 09/010,382,filed Jan. 21, 1998, the complete disclosure of which is incorporatedherein by reference for all purposes.

FIGS. 23-26 illustrate alternative embodiments of the probe 410, eachone incorporating one or more aspiration electrodes positioned in frontof opening 409 of aspiration lumen 425. As shown in FIG. 23, two of theactive electrodes 464 comprise loop electrode 480 that cross over thedistal opening 609. Of course, it will be recognized that a variety ofdifferent configurations are possible, such as a single loop electrode,or multiple loop electrodes having different configurations than shown.In addition, the electrodes may have shapes other than loops, such asthe coiled configurations shown in FIGS. 24 and 25. Alternatively, theelectrodes may be formed within suction lumen proximal to the distalopening 409, as shown in FIG. 26. The main function of loop electrodes480 is to ablate portions of tissue that are drawn into the suctionlumen to prevent clogging of the lumen.

Loop electrodes 4800 are electrically isolated from the other activeelectrodes 464, which can be referred to hereinafter as the ablationelectrodes 464. Loop electrodes 480 may or may not be electricallyisolated from each other. Loop electrodes 480 will usually extend onlyabout 0.05 to 4 mm, preferably about 0.1 to 1 mm from the tissuetreatment surface of electrode support member 464.

In one embodiment, loop electrodes 480 are electrically isolated fromthe other active electrodes 464, and they must be separately activatedat the power supply 28. In other embodiments, loop electrodes 480 willbe activated at the same time that active electrodes 464 are activated.In this case, applicant has found that the plasma layer typically formswhen tissue is drawn adjacent to loop electrodes 480.

Referring now to FIGS. 24 and 25, alternative embodiments for aspirationelectrodes will now be described. As shown in FIG. 24, the aspirationelectrodes may comprise a pair of coiled electrodes 482 that extendacross distal opening 409 of the suction lumen. The larger surface areaof the coiled electrodes 482 usually increases the effectiveness of theelectrodes 482 on tissue fragments passing through opening 409. In FIG.25, the aspiration electrode comprises a single coiled electrode 484passing across the distal opening 409 of suction lumen. This singleelectrode 484 may be sufficient to inhibit clogging of the suctionlumen. Alternatively, the aspiration electrodes may be positioned withinthe suction lumen proximal to the distal opening 609. Preferably, theseelectrodes are close to opening 409 so that tissue does not clog theopening 609 before it reaches electrodes 484. In this embodiment, aseparate return electrode (not shown) may be provided within the suctionlumen to confine the electric currents therein.

Referring to FIG. 26, another embodiment of the present inventionincorporates an aspiration electrode 490 within the aspiration lumen 492of the probe. As shown, the electrode 490 is positioned just proximal ofdistal opening 409 so that the tissue fragments are ablated as theyenter lumen 492. In the representation embodiment, the aspirationelectrode 490 comprises a loop electrode that stretches across theaspiration lumen 492. However, it will be recognized that many otherconfigurations are possible. In this embodiment, the return electrode494 is located outside of the probe as in the previously embodiments.Alternatively, the return electrode(s) may be located within theaspiration lumen 492 with the aspiration electrode 490. For example, theinner insulating coating 493 may be exposed at portions within the lumen492 to provide a conductive path between this exposed portion of returnelectrode 494 and the aspiration electrode 490. The latter embodimenthas the advantage of confining the electric currents to within theaspiration lumen. In addition, in dry fields in which the conductivefluid is delivered to the target site, it is usually easier to maintaina conductive fluid path between the active and return electrodes in thelatter embodiment because the conductive fluid is aspirated through theaspiration lumen 492 along with the tissue fragments.

In use with the present invention, gases will be aspirated throughopening 409 and suction tube 460 (FIG. 21) to a vacuum source. Inaddition, excess electrically conductive fluid, and other fluids (e.g.,blood) will be aspirated from the target site to facilitate thesurgeon's view. Applicant has also found that tissue fragments are alsoaspirated through opening 409 into suction lumen and tube 460 during theprocedure. These tissue fragments are ablated or dissociated with loopelectrodes 480 (FIG. 23) with a similar mechanism described above.Namely, as electrically conductive fluid and tissue fragments areaspirated into loop electrodes 480, these electrodes are activated sothat high frequency voltage is applied to loop electrodes 480 and returnelectrode 462 (of course, the probe may include a different, separatereturn electrode for this purpose). The voltage is sufficient tovaporize the fluid, and create a plasma layer between loop electrodes480 and the tissue fragments so that portions of the tissue fragmentsare ablated or removed. This reduces the volume of the tissue fragmentsas they pass through suction lumen to minimize clogging of the lumen.

In addition, the present invention is particularly useful for removingelastic tissue, such as the synovial tissue found in joints. Inarthroscopic procedures, this elastic synovial tissue tends to move awayfrom instruments within the conductive fluid, making it difficult forconventional instruments to remove this tissue. With the presentinvention, the probe is moved adjacent the target synovial tissue, andthe vacuum source is activated to draw the synovial tissue towards thedistal end of the probe. The aspiration and/or active electrodes arethen energized to ablate this tissue. This allows the surgeon to quicklyand precisely ablate elastic tissue with minimal thermal damage to thetreatment site.

FIGS. 27A-27C schematically illustrate the distal portion of threedifferent embodiments of probe 490 according to the present invention.As shown in 27A, active electrodes 504 are anchored in a support matrix502 of suitable insulating material (e.g., ceramic or glass material,such as alumina, silicon nitride zirconia and the like) which could beformed at the time of manufacture in a flat, hemispherical or othershape according to the requirements of a particular procedure. Thepreferred support matrix material is alumina, available from KyoceraIndustrial Ceramics Corporation, Elkgrove, Illinois, because of its highthermal conductivity, good thermal shock resistance, good electricallyinsulative properties, high flexural modulus, resistance to carbontracking, biocompatibility, and high melting point. The support matrix502 is adhesively joined to a tubular support member 578 that extendsmost or all of the distance between matrix 502 and the proximal end ofprobe 490. Tubular member 578 preferably comprises an electricallyinsulating material, such as an epoxy or silicone-based material.

In a preferred construction technique, active electrodes 504 extendthrough pre-formed openings in the support matrix 502 so that theyprotrude above tissue treatment surface 512 by the desired distance. Theelectrodes are then bonded to the tissue treatment surface 512 ofsupport matrix 502, typically by an inorganic sealing material 580.Sealing material 580 is selected to provide effective electricalinsulation, and good adhesion to both the alumina matrix 502 and theactive electrodes (e.g., titanium, tungsten, molybdenum, platinum,etc.). Sealing material 580 additionally should have a compatiblethermal expansion coefficient and a melting point well below that of themetal active electrodes and the ceramic support matrix, typically beinga glass or glass ceramic.

In the embodiment shown in FIG. 27A, return electrode 512 comprises anannular member positioned around the exterior of shaft 100 of probe 490.Return electrode 512 may fully or partially circumscribe tubular supportmember 578 to form an annular gap 554 therebetween for flow ofelectrically conducting fluid 550 therethrough, as discussed below. Gap554 preferably has a width in the range of 0.1 mm to 4 mm.Alternatively, probe may include a plurality of longitudinal ribsbetween support member 578 and return electrode 512 to form a pluralityof fluid lumens extending along the perimeter of shaft 100. In thisembodiment, the plurality of lumens will extend to a plurality ofopenings.

Return electrode 512 is disposed within an electrically insulativejacket 518, which is typically formed as one or more electricallyinsulative sheaths or coatings, such as polytetrafluoroethylene,polyamide, and the like. The provision of the electrically insulativejacket 518 over return electrode 512 prevents direct electrical contactbetween return electrode 512 and any adjacent body structure. Suchdirect electrical contact between a body structure (e.g., tendon) and anexposed electrode member 512 could result in unwanted heating andnecrosis of the structure at the point of contact causing necrosis.

As shown in FIG. 27A, return electrode 512 is not directly connected toactive electrodes 504. To complete this current path so that terminals504 are electrically connected to return electrode 512, electricallyconducting fluid 550 (e.g., isotonic saline) is caused to flow alongfluid path(s) 583. Fluid path 583 is formed by annular gap 554 betweenouter return electrode 512 and tubular support member 578. Theelectrically conducting fluid 550 flowing through fluid path 583provides a pathway for electrical current flow between active electrodes504 and return electrode 512, as illustrated by the current flux lines560 in FIG. 6A. When a voltage difference is applied between activeelectrodes 504 and return electrode 512, high electric field intensitieswill be generated at the distal tips of terminals 504 with current flowfrom terminals 504 through the target tissue to the return electrode,the high electric field intensities causing ablation of tissue 52 inzone 588.

FIG. 27B illustrates another alternative embodiment of electrosurgicalprobe 490 which has a return electrode 512 positioned within tubularmember 578. Return electrode 512 is preferably a tubular member definingan inner lumen 557 for allowing electrically conducting fluid 550 (e.g.,isotonic saline) to flow therethrough in electrical contact with returnelectrode 512. In this embodiment, a voltage difference is appliedbetween active electrodes 504 and return electrode 512 resulting inelectrical current flow through the electrically conducting fluid 550 asshown by current flux lines 560. As a result of the applied voltagedifference and concomitant high electric field intensities at the tipsof active electrodes 504, tissue 552 becomes ablated or transected inzone 588.

FIG. 27C illustrates another embodiment of probe 490 that is acombination of the embodiments in FIGS. 27A and 27B. As shown, thisprobe includes both an inner lumen 557 and an outer gap or plurality ofouter lumens 554 for flow of electrically conductive fluid. In thisembodiment, the return electrode 512 may be positioned within tubularmember 578 as in FIG. 27B, outside of tubular member 578 as in FIG. 27A,or in both locations.

FIG. 28 illustrates the current flux lines associated with an electricfield 520 applied between the active and return electrodes 504, 512 whena voltage is applied therebetween. As shown, the electric fieldintensity is substantially higher in the region 588 at the tip of theelectrode 504 because the current flux lines are concentrated in theseregions. This high electric field intensity leads to induced molecularbreakdown of the target tissue through molecular dissociation. As aresult of the applied voltage difference between active electrode(s) 504and the target tissue 552(i.e., the voltage gradient across the plasmalayer 524), charged particles (not shown) in the plasma (viz.,electrons) are accelerated towards the tissue. At sufficiently highvoltage differences, these charged particles gain sufficient energy tocause dissociation of the molecular bonds within tissue structures. Thismolecular dissociation is accompanied by the volumetric removal (i.e.,ablative sublimation) of tissue and the production of low molecularweight gases 526, such as oxygen, nitrogen, carbon dioxide, hydrogen andmethane. The short range of the accelerated charged particles within thetissue confines the molecular dissociation process to the surface layerto minimize damage and necrosis to the underlying tissue.

Referring to FIG. 29, the electrosurgical device according to thepresent invention may also be configured as an elongate catheter system600 including portions with sufficient flexibility to permitintroduction into the body and to the target site through one or morevascular lumen(s). As shown, catheter system 600 generally comprises anelectrosurgical catheter 660 connected to a power supply 628 by aninterconnecting cable 686 for providing high frequency voltage to atarget tissue site and an irrigant reservoir or source 600 for providingelectrically conducting fluid to the target site. Catheter 660 generallycomprises an elongate, flexible shaft body 662 including a tissueremoving or ablating region 664 at the distal end of body 662. Theproximal portion of catheter 660 includes a multi-lumen fitment 614which provides for interconnections between lumens and electrical leadswithin catheter 660 and conduits and cables proximal to fitment 614. Byway of example, a catheter electrical connector 696 is removablyconnected to a distal cable connector 694 which, in turn, is removablyconnectable to generator 628 through connector 692. One or moreelectrically conducting lead wires (not shown) within catheter 660extend between one or more active electrodes 663 at tissue ablatingregion 664 and one or more corresponding electrical terminals (also notshown) in catheter connector 696 via active electrode cable branch 687.Similarly, one or more return electrodes 666 at tissue ablating region664 are coupled to a return electrode cable branch 689 of catheterconnector 696 by lead wires (not shown). Of course, a single cablebranch (not shown) may be used for both active and return electrodes.

Catheter body 662 may include reinforcing fibers or braids (not shown)in the walls of at least the distal ablation region 664 of body 662 toprovide responsive torque control for rotation of active electrodesduring tissue engagement. This rigid portion of the catheter body 662preferably extends only about 7 to 10 mm while the remainder of thecatheter body 662 is flexible to provide good trackability duringadvancement and positioning of the electrodes adjacent target tissue.

Conductive fluid 630 is provided to tissue ablation region 664 ofcatheter 660 via a lumen (not shown in FIG. 29) within catheter 660.Fluid is supplied to lumen from the source along a conductive fluidsupply line 602 and a conduit 603, which is coupled to the innercatheter lumen at multi-lumen fitment 614. The source of conductivefluid (e.g., isotonic saline) may be an irrigant pump system (not shown)or a gravity-driven supply, such as an irrigant reservoir 600 positionedseveral feet above the level of the patient. A control valve 604 may bepositioned at the interface of fluid supply line 602 and conduit 603 toallow manual control of the flow rate of electrically conductive fluid630. Alternatively, a metering pump or flow regulator may be used toprecisely control the flow rate of the conductive fluid.

System 600 further includes an aspiration or vacuum system (not shown)to aspirate liquids and gases from the target site. The aspirationsystem will usually comprise a source of vacuum coupled to fitment 614by a aspiration connector 605.

For particular applications, such as for cosmetic surgery on the skin ofthe patient, it may be desirable to achieve volumetric tissue removalwhile maintaining relatively low plasma temperatures, e.g., below 100°C., below 80° C., or even below 50° C. This low temperature tissueremoval reduces the likelihood of collateral thermal damage to thosecells or tissue surrounding the target tissue. Preferably, platinum orplatinum-iridium electrodes are used to maintain the low plasmatemperature. Because platinum has a low resistivity and does notcorrode, the electrical energy is transferred to the conductive liquidin a substantially non-thermal manner.

With a lowered vaporization temperature, the energy levels can bereached while decreasing the thermal energy directed to the tissue. Onetechnique for achieving the desired decrease in temperature ofvolumetric tissue removal is to use an electrically conductive liquidhaving a vaporization temperature below 100° C., or below 80° C.Applicant believes that the temperature of vaporization into a ionizedplasma according to the methods of the present invention is related tothe boiling temperature of the liquid. Boiling temperature of a liquidis defined as the temperature of a liquid at which its vapor pressure isequal to or very slightly greater than the atmospheric or externalpressure of the environment. As is well known, the boiling temperatureof water at sea level (1 atms) is 100° C.

A variety of fluids and/or solutions have boiling temperatures below100° C. For example, methanol has a boiling temperature of 64.7° C.Preferably, the fluid or solution will comprise an electricallyconductive, biocompatible material that is not toxic or harmful to thepatient. In addition, for some applications such as arthroscopy, it isfurther desirable to minimize absorption of the conductive solution intothe surrounding tissue cells. It may further be desirable that theliquid solution be an azeotropic. Azeotropic mixtures of two or moresubstances behave like a single substance in that the vapor produced bypartial evaporation of liquid has the same composition as the liquid.This should prevent the uneven depletion of one solution componentfaster than the other, which may over the course of treatment,undesirably change the boiling temperature.

Another technique for lowering the vaporization temperature of theelectrically conductive fluid involves reducing the external vaporpressure of the air or gas near the target site. As illustrated in thechart of FIG. 30, the boiling temperature of water decreases withdecreases pressure. Thus, by creating a sub-atmospheric environment inthe electrically conductive fluid near the active electrode(s), thetemperature required for vaporization of the fluid will decrease. In oneembodiment shown in FIG. 31, a smaller, compliant chamber or balloon 720can be attached to the area of the patient to be treated. The compliantchamber 720 has sufficient slack to allow the electrosurgical probe 710to move freely about the area covered. Adhesive 722 or other attachmentdevices may be used to secure the chamber 720 to the patient or to theprobe. The chamber may comprise a material such as glass or atransparent polymer that allows for clear viewing of the working end ofthe probe 710. Alternatively, the chamber 720 may include a clear,hardened portion 724 that also functions to maintain the slack in thechamber 720 away from the working end of the probe 710. The hardenedportion 724 may assume a variety of shapes such as dome, cylindrical,circular, and the like.

When the active electrode(s) are activated in a saline solutionaccording to the present invention, the ions in the plasma typicallyfluoresce with a yellow-orange color. It is believed that the colorresults from the excitation of the ionic particles as they areaccelerated towards the target tissue. The color of the fluorescence atleast partly depends on the ionic material included in the solution, asillustrated in FIG. 32. In some embodiments of the present invention, itis preferred that the fluorescence color comprise blue, green, purple oranother color that is not generally associated with conventionalelectrosurgical arcing or other thermal processes. It may be furtherdesirable to simulate the color of excimer laser light to reassure thepatient and user that the process involves cold ablation mechanisms.Accordingly, those compounds having potassium, copper, and barium may beselected. In particular, applicant has found that solutions of potassiumchloride (in the range of about 0.5 to 5%) provide a purple-blue colorthat appears cooler than the orange-yellow color of saline, which isoften associated with conventional electrosurgical arcing.

Preferably, the material used will have ionizing qualities similar tothe sodium chloride used in saline solutions. The concentration of thesematerials will be varied depending on the strength of volumetric tissueremoval desired. Furthermore, spectrophotometric analysis of the plasmacreated using a saline solution reversal is a broad peak near 308 nm(same wavelength as the XeCl excimer laser) and a yet higher peakintensity at 588 nm (giving rise to the yellow/orange color of thesaline plasma). With the proper selection of metal salts or ionicmaterial, more of the wavelength may be concentrated near the 308 nmwavelength of the excimer laser.

Applicant has found that increasing the current densities around theactive electrode(s) can lead to higher energy levels in the ionizedplasma. This, in turn, allows the ionized plasma to break strongermolecular bonds, such as those present in bone or calcified fragments.Since the electrically conductive fluid between the target site andactive electrode(s) is transformed into an ionized vapor layer orplasma, the number of charged particles which can be accelerated againstthe target also determines the removal rate. In addition, theconductivity of the fluid may have an effect on the strength of theplasma field created at the end of the probe. Typically, isotonic salinewith 0.9% concentration of sodium chloride is used with the probe. Byincreasing the sodium chloride concentration to greater than 0.9% andpreferably between about 3% and 20%, the increased concentrationprovides for improved tissue ablation rates. This concept of using ahypertonic saline with enhanced conductivity and increased numbers ofcharged particles is of particular use in bone removal processes or inother procedures requiring aggressive volumetric removal.

Applicant has also found that the plasma layer typically requires ahigher voltage level to initiate a plasma than to sustain the plasmaonce it has been initiated. In addition, it has been found that someconductive solutions facilitate the initiation of the plasma layer,rather than the energy level of the plasma, as discussed above. Forexample, it has been found that saline solutions having concentrationsless than isotonic saline (i.e., less than 0.9% sodium chloride)facilitate the initiation of the plasma layer. This may be useful inapplications where initiation of the plasma layer is more difficult,such as applications where a suction pressure is applied near the activeelectrode(s). A more complete description of this type of application,and the devices that carry out simultaneous suction and ablation can befound in U.S. patent application No. 09/010,382, filed Jan. 21, 1998,the complete disclosure of which is incorporated herein by reference forall purposes.

In another embodiment, the active electrodes are spaced from the tissuea sufficient distance to minimize or avoid contact between the tissueand the vapor layer formed around the active electrodes. In theseembodiments, contact between the heated electrons in the vapor layer andthe tissue is minimized as these electrons travel from the vapor layerback through the conductive fluid to the return electrode. The ionswithin the plasma, however, will have sufficient energy, under certainconditions such as higher voltage levels, to accelerate beyond the vaporlayer to the tissue. Thus, the tissue bonds are dissociated or broken asin previous embodiments, while minimizing the electron flow, and thusthe thermal energy, in contact with the tissue.

FIG. 33 illustrates the working end of electrosurgical probe 900 havinga plurality of active electrodes 958 recessed from a distal surface 960of an insulating support member 948 to prevent contact between activeelectrodes 958 and the tissue 902. Preferably, active electrodes 958will be spaced a sufficient distance to prevent direct contact betweenthe vapor layer 904 formed around terminals 958 and the tissue 902,while allowing ions 906 from the vapor layer 904 to reach the tissue 902for the ablation process described above. This distance will vary withthe voltage applied, the electrode configurations, the ionicconcentration of the conductive fluid and other factors. In therepresentative embodiment, the active electrodes 958 are spaced adistance of about 1.0 mm to 5.0 mm, preferably about 2.0 mm, from distalsurface 960, and the applied voltage is about 200 to 300 volts rms orabout 400 to 600 volts peak to peak (with a square waveform). In thisembodiment, the conductive fluid is isotonic saline, which has a sodiumchloride concentration of about 0.9%. Applicant has found thatincreasing the concentration of sodium chloride or increasing thevoltage applied between the active electrodes and the return electrodeallows use of a higher voltage level. Applicant has further found that ahigher voltage level and more concentration ionic fluid will increasethe concentration and energy level of the ions within the plasma. Byincreasing the distance between the active electrodes and the tissue, ahigher rate of ablation can be achieved without increasing (and in someinstances actually decreasing) the temperature at the tissue level.

As shown in FIG. 33, support member 948 includes an annular extension964 that extends distally from the active electrodes 958 and the innerportion 912 of support member 948. Annular extension 964 will preferablycomprises an electrically insulating material, such as a ceramic orglass composition, and it may comprise a transparent material thatallows the physician to view the plasma chamber 910 formed therein. Inthe representative embodiment, the active electrodes 958 extend distallyfrom the inner portion 912 of support member 948. This configurationincreases the current densities near the edges of active electrodes 948to increase the strength of the plasma 904 and the rate of ablationwhile still maintaining a space between the active electrodes 948 andthe distal surface 960 of annular extension 964. In this embodiment, areturn electrode 920 is positioned proximally of active electrodes 958,and outside of plasma chamber 910. However, the return electrode 920 mayalso be positioned within plasma chamber 910 if it is desired to confinethe electric current to the plasma chamber 910. In this latterconfiguration, the return and active electrodes will be suitableconfigured and spaced to avoid current shorting therebetween.

In the representative embodiment, probe 900 is used in a wet field, orone that is already immersed in conductive fluid. However, it will berecognized that this embodiment may also be used in a dry field, whereinthe conductive fluid is supplied to the target site, e.g., via a fluidlumen or tube within the probe. Preferably, the fluid tube(s) will havedistal opening(s) within the plasma chamber 910 to allow for continualresupply of conductive fluid around active electrodes 958 even if thesurgeon presses the probe against the tissue, which reduces collateraldamage to the tissue. In another embodiment (not shown), the probe willinclude an aspiration lumen (not shown) having a distal opening with theplasma chamber 910 such that excess fluid within the cavity isimmediately aspirated through the lumen. This configuration, togetherwith a return electrode positioned within the plasma chamber 910, allowsthe physician to create a closed fluid and electric circuit thatminimizes fluid and current leakage outside of the plasma chamber 910.

In another embodiment, a screen made of a suitable material that willallow passage of vapor or the plasma layer while substantiallypreventing passage of fluid, such as a synthetic material mesh, closesthe distal opening of the plasma chamber, minimizing the amount of fluidleaking out of the chamber, without significantly restraining the plasmafield.

FIG. 34 illustrates another variation of the inventive device configuredto minimize the collateral heating of target tissue. FIG. 34 illustratesa perspective view of a working end of electrosurgical probe 700. Thisvariation of the invention shares similar features to others describedherein (e.g., a source of electrically conductive fluid and a returnelectrode placed within a fluid path of the conductive fluid, etc.)However, in this variation, the probe 700 includes a plurality of activeelectrodes 702 recessed from a distal surface 704 of an insulatingsupport member 706 to prevent contact between active electrodes 702 andthe target tissue (not shown.) The electrodes 702 of this variation arelocated in individual chambers 708 rather than a single chamber. As withother variations, it may be preferable that active electrodes 702 arerecessed a sufficient distance to prevent direct contact between thevapor layer formed around terminals 702 and the tissue, while allowingthe activated species from the plasma layer to reach the tissue for theablation process described above.

In the variation depicted in FIG. 34, the individual chambers 708 allowfor circulation of the conductive fluid among the active electrodes 702as well as around the device. Circulation of the conductive fluidminimizes accumulation of heat within the fluid, thereby reducingcollateral heating of the target tissue. The variation of FIG. 34 alsoillustrates electrode designs for use with the invention that are suitedto direct current flow. For example, the electrodes 702 may compriseball shaped electrodes which have a reduced surface area 712 at thedistal end of the electrode 702 (e.g., a sharpened point at the end ofthe electrode adjacent to the target tissue.) This configurationincreases the current densities near the edges of the electrodes 702 toincrease the strength of the plasma and the rate of ablation while stillmaintaining a space between the active electrodes 702 and distal surface704 of an insulating support member 706.

FIGS. 35A-35B illustrate another variation of the inventive device whichis configured to minimize undesired heating of the target tissue. FIG.35A illustrates a bottom view of a working end of electrosurgical probe730. As illustrated, the probe 730 contains spacers 736 extending fromthe tissue treatment surface 734 of the probe 730. The spacers 736 mayextend from the tissue treatment surface 734 to the electrodes 732 orbeyond the electrodes 732. In the latter configuration, the spacers 736serve to prevent contact of the electrodes 732 with the tissue beingtreated by the device. Preferably, the spacers 736 create a sufficientdistance between the tissue and the active electrodes 732 to preventdirect contact between the plasma layer formed around electrodeterminals 732 and the tissue while allowing ions from the plasma layerto reach the tissue for the ablation process described above. Asdescribed above, this distance will vary with the voltage applied, theelectrode configurations, the ionic concentration of the conductivefluid and other factors. As is evident, use of the spacers 736 allowsfor circulation of the conductive fluid thereby preventing unwantedaccumulation of heat within the fluid.

It is also noted that, as illustrated in FIGS. 35A, the probe 730 mayinclude electrodes 732 (in this illustration loop electrodes) spacedaround the working end of the probe 730 such that the movement of theprobe 730 in any direction will cause the same pattern of ablation inthe target tissue.

FIG. 35B shows a side view of FIG. 35A, as illustrated, the spacers 736may be selected to have a distance 738 of about 0.025 mm to 0.250 mmbeyond the end of the electrodes 732. It is noted that the spacers 736are not limited to having the same lengths. Moreover, the number ofspacers is not limited to that illustrated, the number may be selectedas required.

FIG. 35B also illustrates the return electrode 740 of the probe 730 asbeing located on a body of the device. As is discussed above, placementof the return electrode 740 is not limited as such. Moreover, also asdiscussed above, a source of conductive fluid (not shown) may beincorporated in the device or may be provided separate from the device.

In some variations of the invention, the spacer 736 may be selected froma rigid or flexible material. When the spacers comprise a flexiblematerial, pushing the working end of the device against the tissuepermits more aggressive treatment or ablation of the tissue. The moreaggressive treatment results from deflection of the flexible spacers 736which permits direct contact between the active electrodes 732 and thetissue. It is also contemplated that the invention may include use offlexible and rigid spacers 736 on the same device. For example, rigidspacers 736 may be selected to be shorter than flexible spacers 736 suchthat pushing the device towards tissue permits deflection of theflexible spacers 736 while the rigid spacers 736 simultaneously limitthe amount of contact between the electrodes 732 and tissue. The spacersmay be made from any medical grade material having sufficientcharacteristics such that it can withstand the temperature and/oroxidation generated by the ablation process. Such materials includesilicone, general plastic elastomers, fluoropolymers (e.g., ETFE, PTFE),ceramics, etc.

FIGS. 36A-36B illustrate variations of the invention in which the probe751 includes an opening 741 in the center of tissue treatment surface742, and a plurality of active electrodes 744 around the perimeter ofsurface 742. FIG. 36A shows a bottom view of the tissue treatmentsurface 742 of the probe. In this variation, the opening 741 functionsas a vent to prevent heat from accumulating adjacent to the tissuetreatment surface 742. The vent/opening 741 may be also configured suchthat the internal profile facilitates the transfer of heat (e.g.,convective, conductive, radiative heat transfer). For example, theinternal profile of the opening 741 may have a draft angle, taper, orother such design to generate a venturi effect. Moreover, it ispreferable that the opening 741 is designed such that heat will not betrapped (e.g., the passage of the opening exits through the side of thedevice opposite to the tissue treatment surface.) Alternatively, theopening may have a separate exhaust port allowing for the venting ofheat. As mentioned herein, it is contemplated that the opening 741 maybe combined with other features of the device (e.g., fluid supplysource, suction ports, return electrode, etc.) while still retaining anexhaust function. Moreover, the venting will permit increased fluidcirculation causing cooling and evacuation of gas bubbles (by productsof tissue ablation). Accordingly, such venting may also increasevisibility at the target site.

Another function of the opening 741 is that the absence of material atthe opening 741 prevents radiated heat (generated by the ablationprocess) from being reflected between the tissue being ablated and thetissue treatment surface 742 of the device. The vent or opening 741allows the heat being generated by the ablation process to escape ratherthan being reflected back to tissue. Without a vent, the radiated heatmay be reflected back onto the tissue from the tissue treatment surfaceof the probe causing undesired collateral heating of the tissue.

FIG. 36B illustrates a side view of the probe of FIG. 36A. As shown inthis view, the device may also contain spacers 746, which, as discussedabove, serve to offset the active electrodes 744 from the tissue. In oneexample, the spacers 746 may be formed from as part of an insert 748(e.g., a silicone molded insert) that is placed within the top of thevent or opening 741 where the spacers 746 are protrusions that extendthrough the tissue treatment surface 742 of the device. FIG. 36B alsoshows the probe as having a return electrode 750 disposed about anoutside of the probe. However, as discussed throughout this disclosure,the placement of the return electrode 750 is not limited as such. Forexample, the return electrode 750 may be placed within the opening 741of the device. Moreover, a fluid source (not shown) may be placed withinthe opening 741, along an outside surface of the probe, or the fluidsource may be external to the device. The opening 741 may also becoupled to a suction port (not shown) as described above.

The devices described herein may also incorporate another feature toreduce the accumulation of heat at the site of the tissue being treated.As discussed above, heat generated by the ablation process may bereflected from the tissue to a tissue treatment surface of the deviceand back to the tissue. To reduce the effects of reflected heat, thedevices of the present invention may incorporate probes having tissuetreatment surfaces or electrode support members that are non-reflective.To accomplish this, materials or coatings may be selected such that heatradiated to the tissue treatment surface or electrode support member isabsorbed or transmitted as opposed to being reflected. For example,glass, ceramic, silicone elastomers, polymer elastomers, siliconnitride, glass used silicon sapphire, may be used as material for theelectrode support member.

While the exemplary embodiment of the present invention has beendescribed in detail, by way of example and for clarity of understanding,a variety of changes, adaptations, and modifications will be obvious tothose of skill in the art. Therefore, the scope of the present inventionis limited solely by the appended claims.

1. A system for applying electrical energy to tissue at a target sitecomprising: an electrosurgical instrument having a shaft with a proximalend, a distal section, a distal end and a substantially planar and solidtissue treatment surface at the distal end, one or more activeelectrodes extending distally from said planar tissue treatment surface,a plurality of spacers extending away from the planar tissue treatmentsurface wherein said spacers extend beyond said one or more electrodessuch that a space remains between said electrodes and said tissue atsaid target site and wherein the spacers extend beyond a distal end ofthe electrodes by a distance between 0.025 mm to 0.25 mm; a returnelectrode arranged at the distal section of the instrument and proximalto said tissue treatment surface; a fluid source for providingelectrically conductive fluid between the return electrode and theactive electrodes; and one or more connectors coupled to the activeelectrodes for connecting the active electrodes to a high frequencypower supply.
 2. The system of claim 1 wherein the spacers are rigid. 3.The system of claim 1 wherein the spacers are flexible.
 4. The system ofclaim 1 further comprising an insert located in a distal end of thedevice and where the spacers protrude from the insert through the tissuetreatment surface.
 5. The system of claim 1 further comprising a ventlocated in the tissue treatment surface.
 6. The system of claim 5wherein the vent is tapered and extends through an end of the instrumentopposite to the tissue treatment surface.
 7. The system of claim 1wherein said active electrode comprises a loop.
 8. The system of claim 1wherein said spacers are discrete.
 9. A system for applying electricalenergy to tissue at a target site comprising: an electrosurgicalinstrument having a shaft with a proximal end, a distal section, adistal end and a substantially planar tissue treatment surface definedat the distal end, at least one bridge-shaped active electrode extendingdistally from said planar tissue treatment surface, a spacer extendingaway from the tissue treatment surface wherein said spacer extendsbeyond said one or more electrodes such that a space remains betweensaid electrodes and said tissue at said target site; a return electrodearranged at the distal section of the instrument and proximal to saidtissue treatment surface; a fluid source for providing electricallyconductive fluid between the return electrode and the active electrodes;and one or more connectors coupled to the active electrodes forconnecting the active electrodes to a high frequency power supply. 10.The system of claim 9 wherein said active electrode comprises a curvefrom an end view.
 11. A method for applying electrical energy to tissueat a target site comprising the steps of: providing an electrosurgicalinstrument having a shaft with a proximal end, a distal section, adistal end and a substantially planar tissue treatment surface definedat the distal end, one or more active electrodes extending distally fromsaid planar tissue treatment surface; applying energy from said activeelectrode to said tissue to modify said tissue; and preventing saidelectrodes from directly contacting said tissue by spacing said activeelectrodes from said tissue with at least one spacer wherein said spacerextends from said tissue treatment surface and beyond said one or moreelectrodes by a distance between 0.025 mm to 0.25 mm such that a spaceremains between said electrodes and said tissue at said target site.